<s>
A	O
botnet	B-Architecture
is	O
a	O
group	O
of	O
Internet-connected	O
devices	O
,	O
each	O
of	O
which	O
runs	O
one	O
or	O
more	O
bots	B-Protocol
.	O
</s>
<s>
Botnets	B-Architecture
can	O
be	O
used	O
to	O
perform	O
Distributed	O
Denial-of-Service	O
(	O
DDoS	O
)	O
attacks	O
,	O
steal	O
data	O
,	O
send	O
spam	O
,	O
and	O
allow	O
the	O
attacker	O
to	O
access	O
the	O
device	O
and	O
its	O
connection	O
.	O
</s>
<s>
The	O
owner	O
can	O
control	O
the	O
botnet	B-Architecture
using	O
command	O
and	O
control	O
(	O
C&C	O
)	O
software	O
.	O
</s>
<s>
The	O
word	O
"	O
botnet	B-Architecture
"	O
is	O
a	O
portmanteau	O
of	O
the	O
words	O
"	O
robot	B-Algorithm
"	O
and	O
"	O
network	B-Architecture
"	O
.	O
</s>
<s>
A	O
botnet	B-Architecture
is	O
a	O
logical	O
collection	O
of	O
Internet-connected	O
devices	O
,	O
such	O
as	O
computers	O
,	O
smartphones	B-Application
or	O
Internet	B-Operating_System
of	I-Operating_System
things	I-Operating_System
(	O
IoT	B-Operating_System
)	O
devices	O
whose	O
security	O
have	O
been	O
breached	O
and	O
control	O
ceded	O
to	O
a	O
third	O
party	O
.	O
</s>
<s>
Each	O
compromised	O
device	O
,	O
known	O
as	O
a	O
"	O
bot	B-Protocol
,	O
"	O
is	O
created	O
when	O
a	O
device	O
is	O
penetrated	O
by	O
software	O
from	O
a	O
malware	O
(	O
malicious	O
software	O
)	O
distribution	O
.	O
</s>
<s>
The	O
controller	O
of	O
a	O
botnet	B-Architecture
is	O
able	O
to	O
direct	O
the	O
activities	O
of	O
these	O
compromised	O
computers	O
through	O
communication	O
channels	O
formed	O
by	O
standards-based	O
network	B-Architecture
protocols	O
,	O
such	O
as	O
IRC	B-Protocol
and	O
Hypertext	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
HTTP	B-Protocol
)	O
.	O
</s>
<s>
Botnets	B-Architecture
are	O
increasingly	O
rented	O
out	O
by	O
cyber	O
criminals	O
as	O
commodities	O
for	O
a	O
variety	O
of	O
purposes	O
.	O
</s>
<s>
Botnet	B-Architecture
architecture	O
has	O
evolved	O
over	O
time	O
in	O
an	O
effort	O
to	O
evade	O
detection	O
and	O
disruption	O
.	O
</s>
<s>
Traditionally	O
,	O
bot	B-Protocol
programs	O
are	O
constructed	O
as	O
clients	B-Operating_System
which	O
communicate	O
via	O
existing	O
servers	O
.	O
</s>
<s>
This	O
allows	O
the	O
bot	B-General_Concept
herder	I-General_Concept
(	O
the	O
controller	O
of	O
the	O
botnet	B-Architecture
)	O
to	O
perform	O
all	O
control	O
from	O
a	O
remote	O
location	O
,	O
which	O
obfuscates	O
the	O
traffic	O
.	O
</s>
<s>
Many	O
recent	O
botnets	B-Architecture
now	O
rely	O
on	O
existing	O
peer-to-peer	O
networks	O
to	O
communicate	O
.	O
</s>
<s>
These	O
P2P	O
bot	B-Protocol
programs	O
perform	O
the	O
same	O
actions	O
as	O
the	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
model	I-Operating_System
,	O
but	O
they	O
do	O
not	O
require	O
a	O
central	O
server	O
to	O
communicate	O
.	O
</s>
<s>
The	O
first	O
botnets	B-Architecture
on	O
the	O
Internet	O
used	O
a	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
model	I-Operating_System
to	O
accomplish	O
their	O
tasks	O
.	O
</s>
<s>
Typically	O
,	O
these	O
botnets	B-Architecture
operate	O
through	O
Internet	B-Protocol
Relay	I-Protocol
Chat	I-Protocol
networks	I-Protocol
,	O
domains	B-Protocol
,	O
or	O
websites	O
.	O
</s>
<s>
Infected	O
clients	B-Operating_System
access	O
a	O
predetermined	O
location	O
and	O
await	O
incoming	O
commands	O
from	O
the	O
server	O
.	O
</s>
<s>
The	O
bot	B-General_Concept
herder	I-General_Concept
sends	O
commands	O
to	O
the	O
server	O
,	O
which	O
relays	O
them	O
to	O
the	O
clients	B-Operating_System
.	O
</s>
<s>
Clients	B-Operating_System
execute	O
the	O
commands	O
and	O
report	O
their	O
results	O
back	O
to	O
the	O
bot	B-General_Concept
herder	I-General_Concept
.	O
</s>
<s>
In	O
the	O
case	O
of	O
IRC	B-Protocol
botnets	B-Architecture
,	O
infected	O
clients	B-Operating_System
connect	O
to	O
an	O
infected	O
IRC	B-Protocol
server	O
and	O
join	O
a	O
channel	O
pre-designated	O
for	O
C&C	O
by	O
the	O
bot	B-General_Concept
herder	I-General_Concept
.	O
</s>
<s>
The	O
bot	B-General_Concept
herder	I-General_Concept
sends	O
commands	O
to	O
the	O
channel	O
via	O
the	O
IRC	B-Protocol
server	O
.	O
</s>
<s>
Clients	B-Operating_System
send	O
messages	O
back	O
to	O
the	O
IRC	B-Protocol
channel	O
with	O
the	O
results	O
of	O
their	O
actions	O
.	O
</s>
<s>
In	O
response	O
to	O
efforts	O
to	O
detect	O
and	O
decapitate	O
IRC	B-Protocol
botnets	B-Architecture
,	O
bot	B-General_Concept
herders	I-General_Concept
have	O
begun	O
deploying	O
malware	O
on	O
peer-to-peer	O
networks	O
.	O
</s>
<s>
These	O
bots	B-Protocol
may	O
use	O
digital	O
signatures	O
so	O
that	O
only	O
someone	O
with	O
access	O
to	O
the	O
private	B-Application
key	I-Application
can	O
control	O
the	O
botnet	B-Architecture
,	O
such	O
as	O
in	O
Gameover	B-Application
ZeuS	I-Application
and	O
the	O
ZeroAccess	O
botnet	B-Architecture
.	O
</s>
<s>
Newer	O
botnets	B-Architecture
fully	O
operate	O
over	O
P2P	O
networks	O
.	O
</s>
<s>
Rather	O
than	O
communicate	O
with	O
a	O
centralized	O
server	O
,	O
P2P	O
bots	B-Protocol
perform	O
as	O
both	O
a	O
command	O
distribution	O
server	O
and	O
a	O
client	O
which	O
receives	O
commands	O
.	O
</s>
<s>
This	O
avoids	O
having	O
any	O
single	O
point	O
of	O
failure	O
,	O
which	O
is	O
an	O
issue	O
for	O
centralized	O
botnets	B-Architecture
.	O
</s>
<s>
In	O
order	O
to	O
find	O
other	O
infected	O
machines	O
,	O
P2P	O
bots	B-Protocol
discreetly	O
probe	O
random	O
IP	B-Protocol
addresses	I-Protocol
until	O
they	O
identify	O
another	O
infected	O
machine	O
.	O
</s>
<s>
The	O
contacted	O
bot	B-Protocol
replies	O
with	O
information	O
such	O
as	O
its	O
software	O
version	O
and	O
list	O
of	O
known	O
bots	B-Protocol
.	O
</s>
<s>
If	O
one	O
of	O
the	O
bots	B-Protocol
 '	O
version	O
is	O
lower	O
than	O
the	O
other	O
,	O
they	O
will	O
initiate	O
a	O
file	O
transfer	O
to	O
update	O
.	O
</s>
<s>
This	O
way	O
,	O
each	O
bot	B-Protocol
grows	O
its	O
list	O
of	O
infected	O
machines	O
and	O
updates	O
itself	O
by	O
periodically	O
communicating	O
to	O
all	O
known	O
bots	B-Protocol
.	O
</s>
<s>
A	O
botnet	B-Architecture
's	O
originator	O
(	O
known	O
as	O
a	O
"	O
bot	B-General_Concept
herder	I-General_Concept
"	O
or	O
"	O
bot	B-General_Concept
master	I-General_Concept
"	O
)	O
controls	O
the	O
botnet	B-Architecture
remotely	O
.	O
</s>
<s>
The	O
program	O
for	O
the	O
operation	O
must	O
communicate	O
via	O
a	O
covert	O
channel	O
to	O
the	O
client	O
on	O
the	O
victim	O
's	O
machine	O
(	O
zombie	B-Application
computer	O
)	O
.	O
</s>
<s>
IRC	B-Protocol
is	O
a	O
historically	O
favored	O
means	O
of	O
C&C	O
because	O
of	O
its	O
communication	O
protocol	O
.	O
</s>
<s>
A	O
bot	B-General_Concept
herder	I-General_Concept
creates	O
an	O
IRC	B-Protocol
channel	O
for	O
infected	O
clients	B-Operating_System
to	O
join	O
.	O
</s>
<s>
The	O
bot	B-General_Concept
herder	I-General_Concept
may	O
set	O
the	O
channel	O
's	O
topic	O
to	O
command	O
the	O
botnet	B-Architecture
.	O
</s>
<s>
For	O
example	O
,	O
the	O
message	O
:herder	O
!	O
herder@example.com	O
TOPIC	O
#channel	O
DDoS	O
www.victim.com	O
from	O
the	O
bot	B-General_Concept
herder	I-General_Concept
alerts	O
all	O
infected	O
clients	B-Operating_System
belonging	O
to	O
#channel	O
to	O
begin	O
a	O
DDoS	O
attack	O
on	O
the	O
website	O
www.victim.com	O
.	O
</s>
<s>
An	O
example	O
response	O
:bot1	O
!	O
bot1@compromised.net	O
PRIVMSG	O
#channel	O
I	O
am	O
DDoSing	O
www.victim.com	O
by	O
a	O
bot	B-Protocol
client	O
alerts	O
the	O
bot	B-General_Concept
herder	I-General_Concept
that	O
it	O
has	O
begun	O
the	O
attack	O
.	O
</s>
<s>
Some	O
botnets	B-Architecture
implement	O
custom	O
versions	O
of	O
well-known	O
protocols	O
.	O
</s>
<s>
The	O
implementation	O
differences	O
can	O
be	O
used	O
for	O
detection	O
of	O
botnets	B-Architecture
.	O
</s>
<s>
For	O
example	O
,	O
Mega-D	O
features	O
a	O
slightly	O
modified	O
Simple	B-Protocol
Mail	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
SMTP	B-Protocol
)	O
implementation	O
for	O
testing	O
spam	O
capability	O
.	O
</s>
<s>
Bringing	O
down	O
the	O
Mega-D	O
'	O
s	O
SMTP	B-Protocol
server	I-Protocol
disables	O
the	O
entire	O
pool	O
of	O
bots	B-Protocol
that	O
rely	O
upon	O
the	O
same	O
SMTP	B-Protocol
server	I-Protocol
.	O
</s>
<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
a	O
zombie	B-Application
computer	O
is	O
a	O
computer	O
connected	O
to	O
the	O
Internet	O
that	O
has	O
been	O
compromised	O
by	O
a	O
hacker	B-Application
,	O
computer	O
virus	O
or	O
trojan	O
horse	O
and	O
can	O
be	O
used	O
to	O
perform	O
malicious	O
tasks	O
under	O
remote	O
direction	O
.	O
</s>
<s>
Botnets	B-Architecture
of	O
zombie	B-Application
computers	O
are	O
often	O
used	O
to	O
spread	O
e-mail	O
spam	O
and	O
launch	O
denial-of-service	O
attacks	O
(	O
DDoS	O
)	O
.	O
</s>
<s>
Most	O
owners	O
of	O
zombie	B-Application
computers	O
are	O
unaware	O
that	O
their	O
system	O
is	O
being	O
used	O
in	O
this	O
way	O
.	O
</s>
<s>
Because	O
the	O
owner	O
tends	O
to	O
be	O
unaware	O
,	O
these	O
computers	O
are	O
metaphorically	O
compared	O
to	O
zombies	B-Application
.	O
</s>
<s>
A	O
coordinated	O
DDoS	O
attack	O
by	O
multiple	O
botnet	B-Architecture
machines	O
also	O
resembles	O
a	O
zombie	B-Application
horde	O
attack	O
.	O
</s>
<s>
The	O
process	O
of	O
stealing	O
computing	O
resources	O
as	O
a	O
result	O
of	O
a	O
system	O
being	O
joined	O
to	O
a	O
"	O
botnet	B-Architecture
"	O
is	O
sometimes	O
referred	O
to	O
as	O
"	O
scrumping	O
"	O
.	O
</s>
<s>
Botnet	B-Architecture
command	O
and	O
control	O
(	O
C&C	O
)	O
protocols	O
have	O
been	O
implemented	O
in	O
a	O
number	O
of	O
ways	O
,	O
from	O
traditional	O
IRC	B-Protocol
approaches	O
to	O
more	O
sophisticated	O
versions	O
.	O
</s>
<s>
Telnet	B-Protocol
botnets	B-Architecture
use	O
a	O
simple	O
C&C	O
botnet	B-Architecture
protocol	O
in	O
which	O
bots	B-Protocol
connect	O
to	O
the	O
main	O
command	O
server	O
to	O
host	O
the	O
botnet	B-Architecture
.	O
</s>
<s>
Bots	B-Protocol
are	O
added	O
to	O
the	O
botnet	B-Architecture
by	O
using	O
a	O
scanning	O
script	B-Language
,	O
which	O
runs	O
on	O
an	O
external	O
server	O
and	O
scans	O
IP	B-Protocol
ranges	I-Protocol
for	O
telnet	B-Protocol
and	O
SSH	B-Protocol
server	O
default	O
logins	O
.	O
</s>
<s>
Once	O
a	O
login	O
is	O
found	O
,	O
the	O
scanning	O
server	O
can	O
infect	O
it	O
through	O
SSH	B-Protocol
with	O
malware	O
,	O
which	O
pings	O
the	O
control	O
server	O
.	O
</s>
<s>
IRC	B-Protocol
networks	I-Protocol
use	O
simple	O
,	O
low	O
bandwidth	O
communication	O
methods	O
,	O
making	O
them	O
widely	O
used	O
to	O
host	O
botnets	B-Architecture
.	O
</s>
<s>
However	O
,	O
in	O
some	O
cases	O
,	O
merely	O
blocking	O
of	O
certain	O
keywords	O
has	O
proven	O
effective	O
in	O
stopping	O
IRC-based	O
botnets	B-Architecture
.	O
</s>
<s>
The	O
RFC	O
1459	O
(	O
IRC	B-Protocol
)	O
standard	O
is	O
popular	O
with	O
botnets	B-Architecture
.	O
</s>
<s>
The	O
first	O
known	O
popular	O
botnet	B-Architecture
controller	O
script	B-Language
,	O
"	O
MaXiTE	O
Bot	B-Protocol
"	O
was	O
using	O
IRC	B-Protocol
XDCC	O
protocol	O
for	O
private	O
control	O
commands	O
.	O
</s>
<s>
One	O
problem	O
with	O
using	O
IRC	B-Protocol
is	O
that	O
each	O
bot	B-Protocol
client	O
must	O
know	O
the	O
IRC	B-Protocol
server	O
,	O
port	O
,	O
and	O
channel	O
to	O
be	O
of	O
any	O
use	O
to	O
the	O
botnet	B-Architecture
.	O
</s>
<s>
Anti-malware	B-Application
organizations	O
can	O
detect	O
and	O
shut	O
down	O
these	O
servers	O
and	O
channels	O
,	O
effectively	O
halting	O
the	O
botnet	B-Architecture
attack	O
.	O
</s>
<s>
If	O
this	O
happens	O
,	O
clients	B-Operating_System
are	O
still	O
infected	O
,	O
but	O
they	O
typically	O
lie	O
dormant	O
since	O
they	O
have	O
no	O
way	O
of	O
receiving	O
instructions	O
.	O
</s>
<s>
To	O
mitigate	O
this	O
problem	O
,	O
a	O
botnet	B-Architecture
can	O
consist	O
of	O
several	O
servers	O
or	O
channels	O
.	O
</s>
<s>
If	O
one	O
of	O
the	O
servers	O
or	O
channels	O
becomes	O
disabled	O
,	O
the	O
botnet	B-Architecture
simply	O
switches	O
to	O
another	O
.	O
</s>
<s>
It	O
is	O
still	O
possible	O
to	O
detect	O
and	O
disrupt	O
additional	O
botnet	B-Architecture
servers	O
or	O
channels	O
by	O
sniffing	O
IRC	B-Protocol
traffic	O
.	O
</s>
<s>
A	O
botnet	B-Architecture
adversary	O
can	O
even	O
potentially	O
gain	O
knowledge	O
of	O
the	O
control	O
scheme	O
and	O
imitate	O
the	O
bot	B-General_Concept
herder	I-General_Concept
by	O
issuing	O
commands	O
correctly	O
.	O
</s>
<s>
Since	O
most	O
botnets	B-Architecture
using	O
IRC	B-Protocol
networks	I-Protocol
and	O
domains	B-Protocol
can	O
be	O
taken	O
down	O
with	O
time	O
,	O
hackers	B-Application
have	O
moved	O
to	O
P2P	O
botnets	B-Architecture
with	O
C&C	O
to	O
make	O
the	O
botnet	B-Architecture
more	O
resilient	O
and	O
resistant	O
to	O
termination	O
.	O
</s>
<s>
Some	O
have	O
also	O
used	O
encryption	O
as	O
a	O
way	O
to	O
secure	O
or	O
lock	O
down	O
the	O
botnet	B-Architecture
from	O
others	O
,	O
most	O
of	O
the	O
time	O
when	O
they	O
use	O
encryption	O
it	O
is	O
public-key	B-Application
cryptography	I-Application
and	O
has	O
presented	O
challenges	O
in	O
both	O
implementing	O
it	O
and	O
breaking	O
it	O
.	O
</s>
<s>
Many	O
large	O
botnets	B-Architecture
tend	O
to	O
use	O
domains	B-Protocol
rather	O
than	O
IRC	B-Protocol
in	O
their	O
construction	O
(	O
see	O
Rustock	O
botnet	B-Architecture
and	O
Srizbi	O
botnet	B-Architecture
)	O
.	O
</s>
<s>
A	O
zombie	B-Application
computer	O
accesses	O
a	O
specially-designed	O
webpage	O
or	O
domain(s )	O
which	O
serves	O
the	O
list	O
of	O
controlling	O
commands	O
.	O
</s>
<s>
The	O
advantages	O
of	O
using	O
web	O
pages	O
or	O
domains	B-Protocol
as	O
C&C	O
is	O
that	O
a	O
large	O
botnet	B-Architecture
can	O
be	O
effectively	O
controlled	O
and	O
maintained	O
with	O
very	O
simple	O
code	O
that	O
can	O
be	O
readily	O
updated	O
.	O
</s>
<s>
Disadvantages	O
of	O
using	O
this	O
method	O
are	O
that	O
it	O
uses	O
a	O
considerable	O
amount	O
of	O
bandwidth	O
at	O
large	O
scale	O
,	O
and	O
domains	B-Protocol
can	O
be	O
quickly	O
seized	O
by	O
government	O
agencies	O
with	O
little	O
effort	O
.	O
</s>
<s>
If	O
the	O
domains	B-Protocol
controlling	O
the	O
botnets	B-Architecture
are	O
not	O
seized	O
,	O
they	O
are	O
also	O
easy	O
targets	O
to	O
compromise	O
with	O
denial-of-service	O
attacks	O
.	O
</s>
<s>
Fast-flux	O
DNS	B-Protocol
can	O
be	O
used	O
to	O
make	O
it	O
difficult	O
to	O
track	O
down	O
the	O
control	O
servers	O
,	O
which	O
may	O
change	O
from	O
day	O
to	O
day	O
.	O
</s>
<s>
Control	O
servers	O
may	O
also	O
hop	O
from	O
DNS	B-Protocol
domain	O
to	O
DNS	B-Protocol
domain	O
,	O
with	O
domain	B-Language
generation	I-Language
algorithms	I-Language
being	O
used	O
to	O
create	O
new	O
DNS	B-Protocol
names	I-Protocol
for	O
controller	O
servers	O
.	O
</s>
<s>
Some	O
botnets	B-Architecture
use	O
free	O
DNS	B-Protocol
hosting	O
services	O
such	O
as	O
DynDns.org,	O
No-IP.com,	O
and	O
Afraid.org	O
to	O
point	O
a	O
subdomain	B-Protocol
towards	O
an	O
IRC	B-Protocol
server	O
that	O
harbors	O
the	O
bots	B-Protocol
.	O
</s>
<s>
While	O
these	O
free	O
DNS	B-Protocol
services	O
do	O
not	O
themselves	O
host	O
attacks	O
,	O
they	O
provide	O
reference	O
points	O
(	O
often	O
hard-coded	O
into	O
the	O
botnet	B-Architecture
executable	O
)	O
.	O
</s>
<s>
Removing	O
such	O
services	O
can	O
cripple	O
an	O
entire	O
botnet	B-Architecture
.	O
</s>
<s>
Calling	O
back	O
to	O
large	O
social	O
media	O
sites	O
such	O
as	O
GitHub	B-Application
,	O
Twitter	B-Application
,	O
Reddit	B-Application
,	O
Instagram	B-Application
,	O
the	O
XMPP	B-Protocol
open	O
source	O
instant	O
message	O
protocol	O
and	O
Tor	B-Application
hidden	O
services	O
are	O
popular	O
ways	O
of	O
avoiding	O
egress	B-Protocol
filtering	I-Protocol
to	O
communicate	O
with	O
a	O
C&C	O
server	O
.	O
</s>
<s>
This	O
example	O
illustrates	O
how	O
a	O
botnet	B-Architecture
is	O
created	O
and	O
used	O
for	O
malicious	O
gain	O
.	O
</s>
<s>
A	O
hacker	B-Application
purchases	O
or	O
builds	O
a	O
Trojan	O
and/or	O
exploit	O
kit	O
and	O
uses	O
it	O
to	O
start	O
infecting	O
users	O
 '	O
computers	O
,	O
whose	O
payload	O
is	O
a	O
malicious	O
application	O
—	O
the	O
bot	B-Protocol
.	O
</s>
<s>
The	O
bot	B-Protocol
instructs	O
the	O
infected	O
PC	O
to	O
connect	O
to	O
a	O
particular	O
command-and-control	O
(	O
C&C	O
)	O
server	O
.	O
</s>
<s>
(	O
This	O
allows	O
the	O
botmaster	B-General_Concept
to	O
keep	O
logs	O
of	O
how	O
many	O
bots	B-Protocol
are	O
active	O
and	O
online	O
.	O
)	O
</s>
<s>
The	O
botmaster	B-General_Concept
may	O
then	O
use	O
the	O
bots	B-Protocol
to	O
gather	O
keystrokes	O
or	O
use	O
form	O
grabbing	O
to	O
steal	O
online	O
credentials	O
and	O
may	O
rent	O
out	O
the	O
botnet	B-Architecture
as	O
DDoS	O
and/or	O
spam	O
as	O
a	O
service	O
or	O
sell	O
the	O
credentials	O
online	O
for	O
a	O
profit	O
.	O
</s>
<s>
Depending	O
on	O
the	O
quality	O
and	O
capability	O
of	O
the	O
bots	B-Protocol
,	O
the	O
value	O
is	O
increased	O
or	O
decreased	O
.	O
</s>
<s>
Newer	O
bots	B-Protocol
can	O
automatically	O
scan	O
their	O
environment	O
and	O
propagate	O
themselves	O
using	O
vulnerabilities	O
and	O
weak	O
passwords	O
.	O
</s>
<s>
Generally	O
,	O
the	O
more	O
vulnerabilities	O
a	O
bot	B-Protocol
can	O
scan	O
and	O
propagate	O
through	O
,	O
the	O
more	O
valuable	O
it	O
becomes	O
to	O
a	O
botnet	B-Architecture
controller	O
community	O
.	O
</s>
<s>
Computers	O
can	O
be	O
co-opted	O
into	O
a	O
botnet	B-Architecture
when	O
they	O
execute	O
malicious	O
software	O
.	O
</s>
<s>
This	O
can	O
be	O
accomplished	O
by	O
luring	O
users	O
into	O
making	O
a	O
drive-by	O
download	O
,	O
exploiting	O
web	B-Protocol
browser	I-Protocol
vulnerabilities	I-Protocol
,	O
or	O
by	O
tricking	O
the	O
user	O
into	O
running	O
a	O
Trojan	O
horse	O
program	O
,	O
which	O
may	O
come	O
from	O
an	O
email	O
attachment	O
.	O
</s>
<s>
This	O
malware	O
will	O
typically	O
install	O
modules	O
that	O
allow	O
the	O
computer	O
to	O
be	O
commanded	O
and	O
controlled	O
by	O
the	O
botnet	B-Architecture
's	O
operator	O
.	O
</s>
<s>
After	O
the	O
software	O
is	O
downloaded	O
,	O
it	O
will	O
call	O
home	O
(	O
send	O
a	O
reconnection	O
packet	B-Protocol
)	O
to	O
the	O
host	O
computer	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
a	O
botnet	B-Architecture
may	O
be	O
temporarily	O
created	O
by	O
volunteer	O
hacktivists	O
,	O
such	O
as	O
with	O
implementations	O
of	O
the	O
Low	B-Language
Orbit	I-Language
Ion	I-Language
Cannon	I-Language
as	O
used	O
by	O
4chan	O
members	O
during	O
Project	B-Algorithm
Chanology	I-Algorithm
in	O
2010	O
.	O
</s>
<s>
China	O
's	O
Great	O
Cannon	O
of	O
China	O
allows	O
the	O
modification	O
of	O
legitimate	O
web	O
browsing	O
traffic	O
at	O
internet	B-General_Concept
backbones	I-General_Concept
into	O
China	O
to	O
create	O
a	O
large	O
ephemeral	O
botnet	B-Architecture
to	O
attack	O
large	O
targets	O
such	O
as	O
GitHub	B-Application
in	O
2015	O
.	O
</s>
<s>
Distributed	O
denial-of-service	O
attacks	O
are	O
one	O
of	O
the	O
most	O
common	O
uses	O
for	O
botnets	B-Architecture
,	O
in	O
which	O
multiple	O
systems	O
submit	O
as	O
many	O
requests	O
as	O
possible	O
to	O
a	O
single	O
Internet	O
computer	O
or	O
service	O
,	O
overloading	O
it	O
and	O
preventing	O
it	O
from	O
servicing	O
legitimate	O
requests	O
.	O
</s>
<s>
The	O
victim	O
's	O
server	O
is	O
bombarded	O
with	O
requests	O
by	O
the	O
bots	B-Protocol
,	O
attempting	O
to	O
connect	O
to	O
the	O
server	O
,	O
therefore	O
,	O
overloading	O
it	O
.	O
</s>
<s>
Google	B-Application
fraud	O
czar	O
Shuman	O
Ghosemajumder	O
has	O
said	O
that	O
these	O
types	O
of	O
attacks	O
causing	O
outages	O
on	O
major	O
websites	O
will	O
continue	O
to	O
occur	O
regularly	O
due	O
the	O
use	O
of	O
botnets	B-Architecture
as	O
a	O
service	O
.	O
</s>
<s>
Compromised	O
machines	O
that	O
are	O
located	O
within	O
a	O
corporate	O
network	B-Architecture
can	O
be	O
worth	O
more	O
to	O
the	O
bot	B-General_Concept
herder	I-General_Concept
,	O
as	O
they	O
can	O
often	O
gain	O
access	O
to	O
confidential	O
corporate	O
information	O
.	O
</s>
<s>
Several	O
targeted	O
attacks	O
on	O
large	O
corporations	O
aimed	O
to	O
steal	O
sensitive	O
information	O
,	O
such	O
as	O
the	O
Aurora	O
botnet	B-Architecture
.	O
</s>
<s>
Ad	O
fraud	O
is	O
often	O
a	O
consequence	O
of	O
malicious	O
bot	B-Protocol
activity	O
,	O
according	O
to	O
CHEQ	O
,	O
Ad	O
Fraud	O
2019	O
,	O
The	O
Economic	O
Cost	O
of	O
Bad	O
Actors	O
on	O
the	O
Internet	O
.	O
</s>
<s>
Commercial	O
purposes	O
of	O
bots	B-Protocol
include	O
influencers	O
using	O
them	O
to	O
boost	O
their	O
supposed	O
popularity	O
,	O
and	O
online	O
publishers	O
using	O
bots	B-Protocol
to	O
increase	O
the	O
number	O
of	O
clicks	O
an	O
ad	O
receives	O
,	O
allowing	O
sites	O
to	O
earn	O
more	O
commission	O
from	O
advertisers	O
.	O
</s>
<s>
Credential	O
stuffing	O
attacks	O
use	O
botnets	B-Architecture
to	O
log	O
in	O
to	O
many	O
user	O
accounts	O
with	O
stolen	O
passwords	O
,	O
such	O
as	O
in	O
the	O
attack	O
against	O
General	O
Motors	O
in	O
2022	O
.	O
</s>
<s>
Bitcoin	B-Protocol
mining	O
was	O
used	O
in	O
some	O
of	O
the	O
more	O
recent	O
botnets	B-Architecture
have	O
which	O
include	O
bitcoin	B-Protocol
mining	O
as	O
a	O
feature	O
in	O
order	O
to	O
generate	O
profits	O
for	O
the	O
operator	O
of	O
the	O
botnet	B-Architecture
.	O
</s>
<s>
Self-spreading	O
functionality	O
,	O
to	O
seek	O
for	O
pre-configured	O
command-and-control	O
(	O
CNC	O
)	O
pushed	O
instruction	O
contains	O
targeted	O
devices	O
or	O
network	B-Architecture
,	O
to	O
aim	O
for	O
more	O
infection	O
,	O
is	O
also	O
spotted	O
in	O
several	O
botnets	B-Architecture
.	O
</s>
<s>
Some	O
of	O
the	O
botnets	B-Architecture
are	O
utilizing	O
this	O
function	O
to	O
automate	O
their	O
infections	O
.	O
</s>
<s>
The	O
botnet	B-Architecture
controller	O
community	O
constantly	O
competes	O
over	O
who	O
has	O
the	O
most	O
bots	B-Protocol
,	O
the	O
highest	O
overall	O
bandwidth	O
,	O
and	O
the	O
most	O
"	O
high-quality	O
"	O
infected	O
machines	O
,	O
like	O
university	O
,	O
corporate	O
,	O
and	O
even	O
government	O
machines	O
.	O
</s>
<s>
While	O
botnets	B-Architecture
are	O
often	O
named	O
after	O
the	O
malware	O
that	O
created	O
them	O
,	O
multiple	O
botnets	B-Architecture
typically	O
use	O
the	O
same	O
malware	O
but	O
are	O
operated	O
by	O
different	O
entities	O
.	O
</s>
<s>
Botnets	B-Architecture
can	O
be	O
used	O
for	O
many	O
electronic	O
scams	O
.	O
</s>
<s>
These	O
botnets	B-Architecture
can	O
be	O
used	O
to	O
distribute	O
malware	O
such	O
as	O
viruses	O
to	O
take	O
control	O
of	O
a	O
regular	O
users	O
computer/software	O
By	O
taking	O
control	O
of	O
someone	O
's	O
personal	O
computer	O
they	O
have	O
unlimited	O
access	O
to	O
their	O
personal	O
information	O
,	O
including	O
passwords	O
and	O
login	O
information	O
to	O
accounts	O
.	O
</s>
<s>
A	O
survey	O
by	O
Verizon	B-Application
found	O
that	O
around	O
two-thirds	O
of	O
electronic	O
"	O
espionage	O
"	O
cases	O
come	O
from	O
phishing	O
.	O
</s>
<s>
The	O
geographic	O
dispersal	O
of	O
botnets	B-Architecture
means	O
that	O
each	O
recruit	O
must	O
be	O
individually	O
identified/corralled/repaired	O
and	O
limits	O
the	O
benefits	O
of	O
filtering	B-Application
.	O
</s>
<s>
Computer	O
security	O
experts	O
have	O
succeeded	O
in	O
destroying	O
or	O
subverting	O
malware	O
command	O
and	O
control	O
networks	O
,	O
by	O
,	O
among	O
other	O
means	O
,	O
seizing	O
servers	O
or	O
getting	O
them	O
cut	O
off	O
from	O
the	O
Internet	O
,	O
denying	O
access	O
to	O
domains	B-Protocol
that	O
were	O
due	O
to	O
be	O
used	O
by	O
malware	O
to	O
contact	O
its	O
C&C	O
infrastructure	O
,	O
and	O
,	O
in	O
some	O
cases	O
,	O
breaking	O
into	O
the	O
C&C	O
network	B-Architecture
itself	O
.	O
</s>
<s>
In	O
response	O
to	O
this	O
,	O
C&C	O
operators	O
have	O
resorted	O
to	O
using	O
techniques	O
such	O
as	O
overlaying	O
their	O
C&C	O
networks	O
on	O
other	O
existing	O
benign	O
infrastructure	O
such	O
as	O
IRC	B-Protocol
or	O
Tor	B-Application
,	O
using	O
peer-to-peer	O
networking	O
systems	O
that	O
are	O
not	O
dependent	O
on	O
any	O
fixed	O
servers	O
,	O
and	O
using	O
public	B-Application
key	I-Application
encryption	I-Application
to	O
defeat	O
attempts	O
to	O
break	O
into	O
or	O
spoof	O
the	O
network	B-Architecture
.	O
</s>
<s>
Norton	B-Application
AntiBot	I-Application
was	O
aimed	O
at	O
consumers	O
,	O
but	O
most	O
target	O
enterprises	O
and/or	O
ISPs	O
.	O
</s>
<s>
Host-based	O
techniques	O
use	O
heuristics	O
to	O
identify	O
bot	B-Protocol
behavior	O
that	O
has	O
bypassed	O
conventional	O
anti-virus	B-Application
software	I-Application
.	O
</s>
<s>
Network-based	O
approaches	O
tend	O
to	O
use	O
the	O
techniques	O
described	O
above	O
;	O
shutting	O
down	O
C&C	O
servers	O
,	O
null-routing	O
DNS	B-Protocol
entries	O
,	O
or	O
completely	O
shutting	O
down	O
IRC	B-Protocol
servers	O
.	O
</s>
<s>
BotHunter	B-Application
is	O
software	O
,	O
developed	O
with	O
support	O
from	O
the	O
U.S.	O
Army	O
Research	O
Office	O
,	O
that	O
detects	O
botnet	B-Architecture
activity	O
within	O
a	O
network	B-Architecture
by	O
analyzing	O
network	B-Architecture
traffic	O
and	O
comparing	O
it	O
to	O
patterns	O
characteristic	O
of	O
malicious	O
processes	O
.	O
</s>
<s>
Researchers	O
at	O
Sandia	O
National	O
Laboratories	O
are	O
analyzing	O
botnets	B-Architecture
 '	O
behavior	O
by	O
simultaneously	O
running	O
one	O
million	O
Linux	O
kernels	O
—	O
a	O
similar	O
scale	O
to	O
a	O
botnet	B-Architecture
—	O
as	O
virtual	B-Architecture
machines	I-Architecture
on	O
a	O
4,480	O
-node	O
high-performance	O
computer	B-Architecture
cluster	I-Architecture
to	O
emulate	O
a	O
very	O
large	O
network	B-Architecture
,	O
allowing	O
them	O
to	O
watch	O
how	O
botnets	B-Architecture
work	O
and	O
experiment	O
with	O
ways	O
to	O
stop	O
them	O
.	O
</s>
<s>
Detecting	O
automated	O
bot	B-Protocol
attacks	O
is	O
becoming	O
more	O
difficult	O
each	O
day	O
as	O
newer	O
and	O
more	O
sophisticated	O
generations	O
of	O
bots	B-Protocol
are	O
getting	O
launched	O
by	O
attackers	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
automated	O
attack	O
can	O
deploy	O
a	O
large	O
bot	B-Protocol
army	O
and	O
apply	O
brute-force	O
methods	O
with	O
highly	O
accurate	O
username	O
and	O
password	O
lists	O
to	O
hack	O
into	O
accounts	O
.	O
</s>
<s>
The	O
idea	O
is	O
to	O
overwhelm	O
sites	O
with	O
tens	O
of	O
thousands	O
of	O
requests	O
from	O
different	O
IPs	O
all	O
over	O
the	O
world	O
,	O
but	O
with	O
each	O
bot	B-Protocol
only	O
submitting	O
a	O
single	O
request	O
every	O
10	O
minutes	O
or	O
so	O
,	O
which	O
can	O
result	O
in	O
more	O
than	O
5	O
million	O
attempts	O
per	O
day	O
.	O
</s>
<s>
In	O
these	O
cases	O
,	O
many	O
tools	O
try	O
to	O
leverage	O
volumetric	O
detection	O
,	O
but	O
automated	O
bot	B-Protocol
attacks	O
now	O
have	O
ways	O
of	O
circumventing	O
triggers	O
of	O
volumetric	O
detection	O
.	O
</s>
<s>
One	O
of	O
the	O
techniques	O
for	O
detecting	O
these	O
bot	B-Protocol
attacks	O
is	O
what	O
's	O
known	O
as	O
"	O
signature-based	O
systems	O
"	O
in	O
which	O
the	O
software	O
will	O
attempt	O
to	O
detect	O
patterns	O
in	O
the	O
request	O
packet	B-Protocol
.	O
</s>
<s>
There	O
is	O
also	O
the	O
behavioral	O
approach	O
to	O
thwarting	O
bots	B-Protocol
,	O
which	O
ultimately	O
tries	O
to	O
distinguish	O
bots	B-Protocol
from	O
humans	O
.	O
</s>
<s>
By	O
identifying	O
non-human	O
behavior	O
and	O
recognizing	O
known	O
bot	B-Protocol
behavior	O
,	O
this	O
process	O
can	O
be	O
applied	O
at	O
the	O
user	O
,	O
browser	O
,	O
and	O
network	B-Architecture
levels	O
.	O
</s>
<s>
On	O
15	O
July	O
2014	O
,	O
the	O
Subcommittee	O
on	O
Crime	O
and	O
Terrorism	O
of	O
the	O
Committee	O
on	O
the	O
Judiciary	O
,	O
United	O
States	O
Senate	O
,	O
held	O
a	O
hearing	O
on	O
the	O
threats	O
posed	O
by	O
botnets	B-Architecture
and	O
the	O
public	O
and	O
private	O
efforts	O
to	O
disrupt	O
and	O
dismantle	O
them	O
.	O
</s>
<s>
The	O
first	O
botnet	B-Architecture
was	O
first	O
acknowledged	O
and	O
exposed	O
by	O
EarthLink	O
during	O
a	O
lawsuit	O
with	O
notorious	O
spammer	O
Khan	O
C	O
.	O
Smith	O
in	O
2001	O
.	O
</s>
<s>
The	O
botnet	B-Architecture
was	O
constructed	O
for	O
the	O
purpose	O
of	O
bulk	O
spam	O
,	O
and	O
accounted	O
for	O
nearly	O
25%	O
of	O
all	O
spam	O
at	O
the	O
time	O
.	O
</s>
<s>
Around	O
2006	O
,	O
to	O
thwart	O
detection	O
,	O
some	O
botnets	B-Architecture
were	O
scaling	O
back	O
in	O
size	O
.	O
</s>
<s>
Researchers	O
at	O
the	O
University	O
of	O
California	O
,	O
Santa	O
Barbara	O
took	O
control	O
of	O
a	O
botnet	B-Architecture
that	O
was	O
six	O
times	O
smaller	O
than	O
expected	O
.	O
</s>
<s>
In	O
some	O
countries	O
,	O
it	O
is	O
common	O
that	O
users	O
change	O
their	O
IP	B-Protocol
address	I-Protocol
a	O
few	O
times	O
in	O
one	O
day	O
.	O
</s>
<s>
Estimating	O
the	O
size	O
of	O
the	O
botnet	B-Architecture
by	O
the	O
number	O
of	O
IP	B-Protocol
addresses	I-Protocol
is	O
often	O
used	O
by	O
researchers	O
,	O
possibly	O
leading	O
to	O
inaccurate	O
assessments	O
.	O
</s>
