<s>
Banner	B-General_Concept
grabbing	I-General_Concept
is	O
a	O
technique	O
used	O
to	O
gain	O
information	O
about	O
a	O
computer	O
system	O
on	O
a	O
network	O
and	O
the	O
services	O
running	O
on	O
its	O
open	O
ports	O
.	O
</s>
<s>
However	O
,	O
an	O
intruder	O
can	O
use	O
banner	B-General_Concept
grabbing	I-General_Concept
in	O
order	O
to	O
find	O
network	B-Device
hosts	I-Device
that	O
are	O
running	O
versions	O
of	O
applications	O
and	O
operating	O
systems	O
with	O
known	O
exploits	O
.	O
</s>
<s>
Some	O
examples	O
of	O
service	B-Protocol
ports	I-Protocol
used	O
for	O
banner	B-General_Concept
grabbing	I-General_Concept
are	O
those	O
used	O
by	O
Hyper	B-Protocol
Text	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
HTTP	B-Protocol
)	O
,	O
File	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
FTP	B-Protocol
)	O
,	O
and	O
Simple	B-Protocol
Mail	I-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
(	O
SMTP	B-Protocol
)	O
;	O
ports	O
80	O
,	O
21	O
,	O
and	O
25	O
respectively	O
.	O
</s>
<s>
Tools	O
commonly	O
used	O
to	O
perform	O
banner	B-General_Concept
grabbing	I-General_Concept
are	O
Telnet	B-Protocol
,	O
Nmap	B-Language
and	O
Netcat	B-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
one	O
could	O
establish	O
a	O
connection	O
to	O
a	O
target	O
web	O
server	O
using	O
Netcat	B-Protocol
,	O
then	O
send	O
an	O
HTTP	B-Protocol
request	O
.	O
</s>
<s>
To	O
prevent	O
this	O
,	O
network	O
administrators	O
should	O
restrict	O
access	O
to	O
services	O
on	O
their	O
networks	O
and	O
shut	O
down	O
unused	O
or	O
unnecessary	O
services	O
running	O
on	O
network	B-Device
hosts	I-Device
.	O
</s>
