<s>
A	O
Browser	B-Application
Helper	I-Application
Object	I-Application
(	O
BHO	O
)	O
is	O
a	O
DLL	B-Library
module	B-Architecture
designed	O
as	O
a	O
plugin	B-Application
for	O
the	O
Microsoft	B-Application
Internet	I-Application
Explorer	I-Application
web	B-Application
browser	I-Application
to	O
provide	O
added	O
functionality	O
.	O
</s>
<s>
BHOs	O
were	O
introduced	O
in	O
October	O
1997	O
with	O
the	O
release	O
of	O
version	B-Protocol
4	I-Protocol
of	O
Internet	B-Application
Explorer	I-Application
.	O
</s>
<s>
Most	O
BHOs	O
are	O
loaded	O
once	O
by	O
each	O
new	O
instance	O
of	O
Internet	B-Application
Explorer	I-Application
.	O
</s>
<s>
However	O
,	O
in	O
the	O
case	O
of	O
Windows	B-Protocol
Explorer	I-Protocol
,	O
a	O
new	O
instance	O
is	O
launched	O
for	O
each	O
window	O
.	O
</s>
<s>
BHOs	O
are	O
still	O
supported	O
as	O
of	O
Windows	O
10	O
,	O
through	O
Internet	B-Application
Explorer	I-Application
11	I-Application
,	O
while	O
BHOs	O
are	O
not	O
supported	O
in	O
Microsoft	B-Application
Edge	I-Application
.	O
</s>
<s>
Each	O
time	O
a	O
new	O
instance	O
of	O
Internet	B-Application
Explorer	I-Application
starts	O
,	O
it	O
checks	O
the	O
Windows	B-Protocol
Registry	I-Protocol
for	O
the	O
key	O
HKEY_LOCAL_MACHINE	O
\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Browser	O
Helper	O
Objects	O
.	O
</s>
<s>
If	O
Internet	B-Application
Explorer	I-Application
finds	O
this	O
key	O
in	O
the	O
registry	O
,	O
it	O
looks	O
for	O
a	O
CLSID	O
key	O
listed	O
below	O
the	O
key	O
.	O
</s>
<s>
The	O
CLSID	O
keys	O
under	O
Browser	B-Application
Helper	I-Application
Objects	I-Application
tell	O
the	O
browser	B-Application
which	O
BHOs	O
to	O
load	O
.	O
</s>
<s>
Removing	O
the	O
registry	B-Protocol
key	I-Protocol
prevents	O
the	O
BHO	O
from	O
being	O
loaded	O
.	O
</s>
<s>
For	O
each	O
CLSID	O
that	O
is	O
listed	O
below	O
the	O
BHO	O
key	O
,	O
Internet	B-Application
Explorer	I-Application
calls	O
CoCreateInstance	O
to	O
start	O
the	O
instance	O
of	O
the	O
BHO	O
in	O
the	O
same	O
process	O
space	O
as	O
the	O
browser	B-Application
.	O
</s>
<s>
If	O
the	O
BHO	O
is	O
started	O
and	O
implements	O
the	O
IObjectWithSite	B-Application
interface	O
,	O
it	O
can	O
control	O
and	O
receive	O
events	O
from	O
Internet	B-Application
Explorer	I-Application
.	O
</s>
<s>
BHOs	O
can	O
be	O
created	O
in	O
any	O
language	O
that	O
supports	O
COM	B-Application
.	O
</s>
<s>
Some	O
modules	B-Architecture
enable	O
the	O
display	O
of	O
different	O
file	O
formats	O
not	O
ordinarily	O
interpretable	O
by	O
the	O
browser	B-Application
.	O
</s>
<s>
The	O
Adobe	B-Application
Acrobat	I-Application
plug-in	B-Application
that	O
allows	O
Internet	B-Application
Explorer	I-Application
users	O
to	O
read	O
PDF	B-Application
files	I-Application
within	O
their	O
browser	B-Application
is	O
a	O
BHO	O
.	O
</s>
<s>
Other	O
modules	B-Architecture
add	O
toolbars	O
to	O
Internet	B-Application
Explorer	I-Application
,	O
such	O
as	O
the	O
Alexa	B-Protocol
Toolbar	I-Protocol
that	O
provides	O
a	O
list	O
of	O
web	O
sites	O
related	O
to	O
the	O
one	O
you	O
are	O
currently	O
browsing	O
,	O
or	O
the	O
Google	B-Protocol
Toolbar	I-Protocol
that	O
adds	O
a	O
toolbar	O
with	O
a	O
Google	O
search	O
box	O
to	O
the	O
browser	B-Application
user	B-Application
interface	I-Application
.	O
</s>
<s>
The	O
Conduit	O
toolbars	O
are	O
based	O
on	O
a	O
BHO	O
that	O
can	O
be	O
used	O
on	O
Internet	B-Application
Explorer	I-Application
7	I-Application
and	O
up	O
.	O
</s>
<s>
This	O
BHO	O
provides	O
a	O
search	O
facility	O
that	O
connects	O
to	O
Microsoft	O
's	O
Bing	B-Application
search	I-Application
.	O
</s>
<s>
The	O
BHO	O
API	B-Application
exposes	O
hooks	O
that	O
allow	O
the	O
BHO	O
to	O
access	O
the	O
Document	B-General_Concept
Object	I-General_Concept
Model	I-General_Concept
(	O
DOM	B-General_Concept
)	O
of	O
the	O
current	O
page	O
and	O
to	O
control	O
navigation	O
.	O
</s>
<s>
Because	O
BHOs	O
have	O
unrestricted	O
access	O
to	O
the	O
Internet	B-Application
Explorer	I-Application
event	O
model	O
,	O
some	O
forms	O
of	O
malware	O
have	O
also	O
been	O
created	O
as	O
BHOs	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
Download.ject	B-Application
malware	O
is	O
a	O
BHO	O
that	O
is	O
activated	O
when	O
a	O
secure	O
HTTP	B-Protocol
connection	O
is	O
made	O
to	O
a	O
financial	O
institution	O
,	O
then	O
begins	O
to	O
record	O
keystrokes	O
for	O
the	O
purpose	O
of	O
capturing	O
user	O
passwords	O
.	O
</s>
<s>
The	O
C2.LOP	B-Application
malware	O
adds	O
links	O
and	O
popups	O
of	O
its	O
own	O
to	O
web	O
pages	O
in	O
order	O
to	O
drive	O
users	O
to	O
pay-per-click	O
websites	O
.	O
</s>
<s>
Many	O
BHOs	O
introduce	O
visible	O
changes	O
to	O
a	O
browser	B-Application
's	O
interface	O
,	O
such	O
as	O
installing	O
toolbars	O
in	O
Internet	B-Application
Explorer	I-Application
and	O
the	O
like	O
,	O
but	O
others	O
run	O
without	O
any	O
change	O
to	O
the	O
interface	O
.	O
</s>
<s>
This	O
renders	O
it	O
easy	O
for	O
malicious	O
coders	O
to	O
conceal	O
the	O
actions	O
of	O
their	O
browser	B-Protocol
add-on	I-Protocol
,	O
especially	O
since	O
,	O
after	O
being	O
installed	O
,	O
the	O
BHO	O
seldom	O
requires	O
permission	O
before	O
performing	O
further	O
actions	O
.	O
</s>
<s>
The	O
DyFuCA	B-Application
spyware	O
even	O
replaces	O
Internet	B-Application
Explorer	I-Application
's	O
general	O
error	O
page	O
with	O
an	O
ad	O
page	O
.	O
</s>
<s>
In	O
response	O
to	O
the	O
problems	O
associated	O
with	O
BHOs	O
and	O
similar	O
extensions	O
to	O
Internet	B-Application
Explorer	I-Application
,	O
Microsoft	O
debuted	O
an	O
Add-on	B-Operating_System
Manager	O
in	O
Internet	B-Application
Explorer	I-Application
6	I-Application
with	O
the	O
release	O
of	O
Service	O
Pack	O
2	O
for	O
Windows	B-Application
XP	I-Application
(	O
updating	O
it	O
to	O
IE6	B-Application
Security	O
Version	O
1	O
,	O
a.k.a.	O
</s>
<s>
This	O
utility	O
displays	O
a	O
list	O
of	O
all	O
installed	O
BHOs	O
,	O
browser	B-Protocol
extensions	I-Protocol
and	O
ActiveX	B-Application
controls	I-Application
,	O
and	O
allows	O
the	O
user	O
to	O
enable	O
or	O
disable	O
them	O
at	O
will	O
.	O
</s>
<s>
Spybot	B-Application
S&D	I-Application
advanced	O
mode	O
has	O
a	O
similar	O
tool	O
built	O
in	O
to	O
allow	O
the	O
user	O
to	O
disable	O
installed	O
BHO	O
.	O
</s>
