<s>
TrustRank	B-Application
is	O
an	O
algorithm	O
that	O
conducts	O
link	B-Application
analysis	I-Application
to	O
separate	O
useful	O
webpages	O
from	O
spam	O
and	O
helps	O
search	B-Application
engine	I-Application
rank	O
pages	O
in	O
SERPs	O
(	O
Search	B-Application
Engine	I-Application
Results	O
Pages	O
)	O
.	O
</s>
<s>
Search	B-Application
engines	I-Application
have	O
many	O
different	O
algorithms	O
and	O
ranking	O
factors	O
that	O
they	O
use	O
when	O
measuring	O
the	O
quality	O
of	O
webpages	O
.	O
</s>
<s>
TrustRank	B-Application
is	O
one	O
of	O
them	O
.	O
</s>
<s>
Because	O
manual	O
review	O
of	O
the	O
Internet	O
is	O
impractical	O
and	O
very	O
expensive	O
,	O
TrustRank	B-Application
was	O
introduced	O
in	O
order	O
to	O
help	O
achieve	O
this	O
task	O
much	O
faster	O
and	O
cheaper	O
.	O
</s>
<s>
It	O
was	O
first	O
introduced	O
by	O
researchers	O
Zoltan	O
Gyongyi	O
and	O
Hector	O
Garcia-Molina	O
of	O
Stanford	O
University	O
and	O
Jan	O
Pedersen	O
of	O
Yahoo	B-Application
!	I-Application
</s>
<s>
in	O
their	O
paper	O
"	O
Combating	O
Web	O
Spam	O
with	O
TrustRank	B-Application
"	O
in	O
2004	O
.	O
</s>
<s>
Today	O
,	O
this	O
algorithm	O
is	O
a	O
part	O
of	O
major	O
web	B-Application
search	I-Application
engines	I-Application
like	O
Yahoo	B-Application
!	I-Application
</s>
<s>
and	O
Google	B-Application
.	I-Application
</s>
<s>
One	O
of	O
the	O
most	O
important	O
factors	O
that	O
help	O
web	B-Application
search	I-Application
engine	I-Application
determine	O
the	O
quality	O
of	O
a	O
web	O
page	O
when	O
returning	O
results	O
are	O
backlinks	O
.	O
</s>
<s>
Search	B-Application
engines	I-Application
take	O
a	O
number	O
and	O
quality	O
of	O
backlinks	O
into	O
consideration	O
when	O
assigning	O
a	O
place	O
to	O
a	O
certain	O
web	O
page	O
in	O
SERPs	O
.	O
</s>
<s>
Many	O
web	O
spam	O
pages	O
are	O
created	O
only	O
with	O
the	O
intention	O
of	O
misleading	O
search	B-Application
engines	I-Application
.	O
</s>
<s>
These	O
pages	O
,	O
chiefly	O
created	O
for	O
commercial	O
reasons	O
,	O
use	O
various	O
techniques	O
to	O
achieve	O
higher-than-deserved	O
rankings	O
in	O
the	O
search	B-Application
engines	I-Application
 '	O
result	O
pages	O
.	O
</s>
<s>
While	O
human	O
experts	O
can	O
easily	O
identify	O
spam	O
,	O
search	B-Application
engines	I-Application
are	O
still	O
being	O
improved	O
daily	O
in	O
order	O
to	O
do	O
it	O
without	O
help	O
of	O
humans	O
.	O
</s>
<s>
Google	B-Application
's	I-Application
PageRank	B-Algorithm
and	O
other	O
search	O
ranking	O
algorithms	O
have	O
been	O
subjected	O
to	O
such	O
manipulation	O
.	O
</s>
<s>
TrustRank	B-Application
seeks	O
to	O
combat	O
spam	O
by	O
filtering	O
the	O
web	O
based	O
upon	O
reliability	O
.	O
</s>
<s>
TrustRank	B-Application
's	O
reliability	O
diminishes	O
with	O
increased	O
distance	O
between	O
documents	O
and	O
the	O
seed	O
set	O
.	O
</s>
<s>
The	O
researchers	O
who	O
proposed	O
the	O
TrustRank	B-Application
methodology	O
have	O
continued	O
to	O
refine	O
their	O
work	O
by	O
evaluating	O
related	O
topics	O
,	O
such	O
as	O
measuring	O
spam	O
mass	O
.	O
</s>
