<s>
In	O
computer	B-Architecture
networking	I-Architecture
,	O
a	O
packet	B-Protocol
drop	I-Protocol
attack	I-Protocol
or	O
blackhole	B-Protocol
attack	I-Protocol
is	O
a	O
type	O
of	O
denial-of-service	O
attack	O
in	O
which	O
a	O
router	O
that	O
is	O
supposed	O
to	O
relay	O
packets	B-Protocol
instead	O
discards	B-Protocol
them	O
.	O
</s>
<s>
Because	O
packets	B-Protocol
are	O
routinely	O
dropped	O
from	O
a	O
lossy	O
network	O
,	O
the	O
packet	B-Protocol
drop	I-Protocol
attack	I-Protocol
is	O
very	O
hard	O
to	O
detect	O
and	O
prevent	O
.	O
</s>
<s>
by	O
dropping	O
packets	B-Protocol
for	O
a	O
particular	O
network	O
destination	O
,	O
at	O
a	O
certain	O
time	O
of	O
the	O
day	O
,	O
a	O
packet	B-Protocol
every	O
n	O
packets	B-Protocol
or	O
every	O
t	O
seconds	O
,	O
or	O
a	O
randomly	O
selected	O
portion	O
of	O
the	O
packets	B-Protocol
.	O
</s>
<s>
If	O
the	O
malicious	O
router	O
attempts	O
to	O
drop	O
all	O
packets	B-Protocol
that	O
come	O
in	O
,	O
the	O
attack	O
can	O
actually	O
be	O
discovered	O
fairly	O
quickly	O
through	O
common	O
networking	O
tools	O
such	O
as	O
traceroute	O
.	O
</s>
<s>
However	O
,	O
if	O
the	O
malicious	O
router	O
begins	O
dropping	O
packets	B-Protocol
on	O
a	O
specific	O
time	O
period	O
or	O
over	O
every	O
n	O
packets	B-Protocol
,	O
it	O
is	O
often	O
harder	O
to	O
detect	O
because	O
some	O
traffic	O
still	O
flows	O
across	O
the	O
network	O
.	O
</s>
<s>
The	O
packet	B-Protocol
drop	I-Protocol
attack	I-Protocol
can	O
be	O
frequently	O
deployed	O
to	O
attack	O
wireless	B-General_Concept
ad	I-General_Concept
hoc	I-General_Concept
networks	I-General_Concept
.	O
</s>
<s>
By	O
doing	O
this	O
,	O
all	O
traffic	O
will	O
be	O
directed	O
to	O
the	O
host	O
that	O
has	O
been	O
compromised	O
,	O
and	O
the	O
host	O
is	O
able	O
to	O
drop	B-Protocol
packets	I-Protocol
at	O
will	O
.	O
</s>
<s>
Also	O
over	O
a	O
mobile	B-Protocol
ad	I-Protocol
hoc	I-Protocol
network	I-Protocol
,	O
hosts	O
are	O
specifically	O
vulnerable	O
to	O
collaborative	O
attacks	O
where	O
multiple	O
hosts	O
will	O
become	O
compromised	O
and	O
deceive	O
the	O
other	O
hosts	O
on	O
the	O
network	O
.	O
</s>
