<s>
A	O
personal	B-Protocol
firewall	I-Protocol
is	O
an	O
application	B-Application
which	O
controls	O
network	B-Architecture
traffic	O
to	O
and	O
from	O
a	O
computer	O
,	O
permitting	O
or	O
denying	O
communications	O
based	O
on	O
a	O
security	O
policy	O
.	O
</s>
<s>
Typically	O
it	O
works	O
as	O
an	O
application	B-Protocol
layer	I-Protocol
firewall	I-Protocol
.	O
</s>
<s>
A	O
personal	B-Protocol
firewall	I-Protocol
differs	O
from	O
a	O
conventional	O
firewall	B-Application
in	O
terms	O
of	O
scale	O
.	O
</s>
<s>
A	O
personal	B-Protocol
firewall	I-Protocol
will	O
usually	O
protect	O
only	O
the	O
computer	O
on	O
which	O
it	O
is	O
installed	O
,	O
as	O
compared	O
to	O
a	O
conventional	O
firewall	B-Application
which	O
is	O
normally	O
installed	O
on	O
a	O
designated	O
interface	O
between	O
two	O
or	O
more	O
networks	O
,	O
such	O
as	O
a	O
router	B-Protocol
or	O
proxy	B-Application
server	I-Application
.	O
</s>
<s>
Hence	O
,	O
personal	B-Protocol
firewalls	I-Protocol
allow	O
a	O
security	O
policy	O
to	O
be	O
defined	O
for	O
individual	O
computers	O
,	O
whereas	O
a	O
conventional	O
firewall	B-Application
controls	O
the	O
policy	O
between	O
the	O
networks	O
that	O
it	O
connects	O
.	O
</s>
<s>
The	O
per-computer	O
scope	O
of	O
personal	B-Protocol
firewalls	I-Protocol
is	O
useful	O
to	O
protect	O
machines	O
that	O
are	O
moved	O
across	O
different	O
networks	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
laptop	B-Device
computer	I-Device
may	O
be	O
used	O
on	O
a	O
trusted	O
intranet	B-General_Concept
at	O
a	O
workplace	O
where	O
minimal	O
protection	O
is	O
needed	O
as	O
a	O
conventional	O
firewall	B-Application
is	O
already	O
in	O
place	O
,	O
and	O
services	O
that	O
require	O
open	O
ports	O
such	O
as	O
file	O
and	O
printer	O
sharing	O
are	O
useful	O
.	O
</s>
<s>
The	O
same	O
laptop	B-Device
could	O
be	O
used	O
at	O
public	O
Wi-Fi	B-Application
hotspots	I-Application
,	O
where	O
it	O
may	O
be	O
necessary	O
to	O
decide	O
the	O
level	O
of	O
trust	O
and	O
reconfigure	O
firewall	B-Application
settings	O
to	O
limit	O
traffic	O
to	O
and	O
from	O
the	O
computer	O
.	O
</s>
<s>
A	O
firewall	B-Application
can	O
be	O
configured	O
to	O
allow	O
different	O
security	O
policies	O
for	O
each	O
network	B-Architecture
.	O
</s>
<s>
Unlike	O
network	B-Application
firewalls	I-Application
,	O
many	O
personal	B-Protocol
firewalls	I-Protocol
are	O
able	O
to	O
control	O
network	B-Architecture
traffic	O
allowed	O
to	O
programs	B-Application
on	O
the	O
secured	O
computer	O
.	O
</s>
<s>
When	O
an	O
application	B-Application
attempts	O
an	O
outbound	O
connection	O
,	O
the	O
firewall	B-Application
may	O
block	O
it	O
if	O
blacklisted	O
,	O
or	O
ask	O
the	O
user	O
whether	O
to	O
blacklist	O
it	O
if	O
it	O
is	O
not	O
yet	O
known	O
.	O
</s>
<s>
Personal	B-Protocol
firewalls	I-Protocol
may	O
also	O
provide	O
some	O
level	O
of	O
intrusion	O
detection	O
,	O
allowing	O
the	O
software	O
to	O
terminate	O
or	O
block	O
connectivity	O
where	O
it	O
suspects	O
an	O
intrusion	O
is	O
being	O
attempted	O
.	O
</s>
<s>
Common	O
personal	B-Protocol
firewall	I-Protocol
features	O
:	O
</s>
<s>
Allows	O
the	O
user	O
to	O
control	O
which	O
programs	B-Application
can	O
and	O
cannot	O
access	O
the	O
local	B-General_Concept
network	I-General_Concept
and/or	O
Internet	O
and	O
provide	O
the	O
user	O
with	O
information	O
about	O
an	O
application	B-Application
that	O
makes	O
a	O
connection	O
attempt	O
.	O
</s>
<s>
Hide	O
the	O
computer	O
from	O
port	O
scans	O
by	O
not	O
responding	O
to	O
unsolicited	O
network	B-Architecture
traffic	O
.	O
</s>
<s>
Prevent	O
unwanted	O
network	B-Architecture
traffic	O
from	O
locally	O
installed	O
applications	O
.	O
</s>
<s>
Provide	O
information	O
about	O
the	O
destination	O
server	B-Application
with	O
which	O
an	O
application	B-Application
is	O
attempting	O
to	O
communicate	O
.	O
</s>
<s>
Firewalls	B-Application
help	O
protecting	O
internal	B-General_Concept
network	I-General_Concept
from	O
hackers	O
,	O
However	O
firewall	B-Application
do	O
have	O
some	O
limitations	O
.	O
</s>
<s>
If	O
the	O
system	O
has	O
been	O
compromised	O
by	O
malware	O
,	O
spyware	O
or	O
similar	O
software	O
,	O
these	O
programs	B-Application
can	O
also	O
manipulate	O
the	O
firewall	B-Application
,	O
because	O
both	O
are	O
running	O
on	O
the	O
same	O
system	O
.	O
</s>
<s>
It	O
may	O
be	O
possible	O
to	O
bypass	O
or	O
even	O
completely	O
shut	O
down	O
software	O
firewalls	B-Application
in	O
such	O
a	O
manner	O
.	O
</s>
<s>
A	O
firewall	B-Application
ca	O
n't	O
notify	O
,	O
if	O
it	O
has	O
been	O
incorrectly	O
configured	O
.	O
</s>
<s>
Firewall	B-Application
may	O
limit	O
access	O
from	O
the	O
Internet	O
,	O
but	O
it	O
may	O
not	O
protect	O
your	O
network	B-Architecture
from	O
wireless	O
and	O
other	O
access	O
to	O
your	O
systems	O
.	O
</s>
<s>
Firewalls	B-Application
and	O
Virtual	B-Application
Private	I-Application
Networks	I-Application
are	O
not	O
the	O
only	O
solution	O
to	O
secure	O
private	O
documents	O
and	O
emails	O
that	O
are	O
either	O
sent	O
within	O
an	O
organization	O
or	O
to	O
other	O
business	O
contacts	O
that	O
are	O
outside	O
the	O
organization	O
.	O
</s>
<s>
Software	O
firewalls	B-Application
that	O
interface	O
with	O
the	O
operating	O
system	O
or	O
with	O
other	O
firewalls	B-Application
or	O
security	O
software	O
at	O
the	O
kernel	O
mode	O
level	O
may	O
potentially	O
cause	O
instability	O
and/or	O
introduce	O
security	O
flaws	O
.	O
</s>
<s>
In	O
the	O
mid	O
1990s	O
,	O
as	O
a	O
part	O
of	O
the	O
information	O
security	O
architecture	O
project	O
for	O
a	O
Fortune	O
100	O
corporation	O
in	O
the	O
United	O
States	O
(	O
the	O
Anheuser-Busch	O
Corporation	O
)	O
,	O
one	O
of	O
the	O
members	O
of	O
the	O
three-man	O
architectural	O
development	O
team	O
came	O
up	O
with	O
a	O
concept	O
with	O
regards	O
to	O
improving	O
the	O
overall	O
security	O
of	O
the	O
operating	O
system	O
to	O
be	O
used	O
on	O
all	O
the	O
computers	O
within	O
this	O
networked	O
system	O
(	O
a	O
network	B-Architecture
system	O
referred	O
to	O
as	O
BudNET	O
)	O
.	O
</s>
<s>
Donald	O
R	O
.	O
Woeltje	O
Jr.	O
and	O
the	O
concept	O
he	O
came	O
up	O
with	O
was	O
the	O
installation	O
of	O
special	O
software	O
(	O
firewall	B-Application
software	I-Application
)	O
on	O
every	O
BudNET	O
server	B-Application
,	O
workstation	O
,	O
and	O
perimeter	O
security	O
device	O
.	O
</s>
<s>
Indeed	O
,	O
every	O
single	O
Windows	B-Application
system	O
on	O
the	O
BudNET	O
network	B-Architecture
.	O
</s>
<s>
This	O
is	O
a	O
concept	O
that	O
is	O
now	O
commonly	O
referred	O
to	O
as	O
"	O
personal	B-Protocol
firewall	I-Protocol
"	O
software	O
.	O
</s>
<s>
Woeltje	O
did	O
not	O
invent	O
personal	B-Protocol
firewall	I-Protocol
software	O
,	O
he	O
did	O
invent	O
the	O
idea	O
of	O
the	O
"	O
personal	O
firewall.	O
"	O
</s>
<s>
Woeltje	O
brought	O
in	O
all	O
the	O
leading	O
firewall	B-Application
vendors	O
for	O
meetings	O
concerning	O
the	O
products	O
being	O
considered	O
for	O
use	O
for	O
the	O
perimeter	O
security	O
of	O
the	O
BudNET	O
network	B-Architecture
,	O
SSgt	O
.	O
</s>
<s>
Woeltje	O
brought	O
up	O
the	O
concept	O
of	O
the	O
"	O
personal	B-Protocol
firewall	I-Protocol
"	O
with	O
the	O
vendors	O
and	O
asked	O
them	O
if	O
they	O
had	O
any	O
firewall	B-Application
product	O
that	O
could	O
be	O
used	O
in	O
this	O
way	O
.	O
</s>
<s>
With	O
the	O
exception	O
of	O
the	O
representatives	O
from	O
the	O
Cyberguard	O
Corporation	O
,	O
every	O
vendor	O
said	O
that	O
not	O
only	O
did	O
that	O
not	O
have	O
any	O
firewall	B-Application
software	I-Application
that	O
could	O
be	O
used	O
in	O
this	O
way	O
but	O
they	O
also	O
said	O
that	O
the	O
idea	O
was	O
crazy	O
and	O
unworkable	O
.	O
</s>
<s>
But	O
,	O
today	O
we	O
know	O
they	O
were	O
wrong	O
because	O
the	O
use	O
of	O
personal	B-Protocol
firewall	I-Protocol
software	O
has	O
become	O
a	O
de	O
facto	O
computer	O
security	O
standard	O
.	O
</s>
<s>
Woeltje	O
discussed	O
"	O
personal	B-Protocol
firewall	I-Protocol
"	O
software	O
with	O
were	O
,	O
among	O
others	O
,	O
Cisco	O
,	O
Checkpoint	O
,	O
Axent	O
Technologies	O
,	O
Milkyway	O
Networks	O
,	O
Cyberguard	O
,	O
Network	B-Architecture
ONE	O
,	O
Trusted	O
Information	O
Systems	O
,	O
and	O
Secure	O
Computing	O
Corporation	O
.	O
</s>
