<s>
p0f	B-Protocol
is	O
a	O
passive	O
TCP/IP	B-Protocol
stack	I-Protocol
fingerprinting	I-Protocol
tool	O
.	O
</s>
<s>
p0f	B-Protocol
can	O
attempt	O
to	O
identify	O
the	O
system	O
running	O
on	O
machines	O
that	O
send	O
network	O
traffic	O
to	O
the	O
box	O
it	O
is	O
running	O
on	O
,	O
or	O
to	O
a	O
machine	O
that	O
shares	B-Protocol
a	I-Protocol
medium	I-Protocol
with	O
the	O
machine	O
it	O
is	O
running	O
on	O
.	O
</s>
<s>
p0f	B-Protocol
can	O
also	O
assist	O
in	O
analysing	O
other	O
aspects	O
of	O
the	O
remote	O
system	O
.	O
</s>
<s>
By	O
inspecting	O
network	O
traffic	O
passively	O
,	O
p0f	B-Protocol
can	O
attempt	O
to	O
identify	O
the	O
operating	O
systems	O
on	O
remote	O
machines	O
that	O
send	O
TCP	O
packets	O
to	O
the	O
detecting	O
machine	O
's	O
network	O
interface	O
,	O
or	O
to	O
a	O
physical	O
subnet	O
that	O
the	O
detecting	O
machine	O
can	O
listen	O
on	O
.	O
</s>
<s>
Since	O
version	O
3	O
,	O
p0f	B-Protocol
is	O
also	O
able	O
to	O
deduce	O
aspects	O
of	O
the	O
remote	O
system	O
by	O
inspecting	O
application-level	O
HTTP	O
messages	O
.	O
</s>
<s>
p0f	B-Protocol
can	O
also	O
check	O
for	O
firewall	O
presence	O
.	O
</s>
<s>
Unlike	O
tools	O
like	O
nmap	B-Language
,	O
p0f	B-Protocol
does	O
not	O
generate	O
traffic	O
.	O
</s>
<s>
This	O
allows	O
them	O
to	O
be	O
modified	O
without	O
recompiling	O
p0f	B-Protocol
.	O
</s>
<s>
The	O
user	O
is	O
allowed	O
to	O
use	O
a	O
different	O
fingerprinting	O
file	O
by	O
selecting	O
another	O
one	O
at	O
run	B-Library
time	I-Library
.	O
</s>
<s>
p0f	B-Protocol
does	O
not	O
use	O
a	O
graphical	O
user	O
interface	O
:	O
it	O
is	O
run	O
from	O
the	O
command	B-Application
line	I-Application
prompt	O
.	O
</s>
