<s>
Domain	B-Application
Name	I-Application
System	I-Application
blocking	I-Application
,	O
or	O
DNS	B-Application
blocking	I-Application
/	O
filtering	O
is	O
a	O
strategy	O
for	O
making	O
it	O
difficult	O
for	O
users	O
to	O
locate	O
specific	O
domains	O
or	O
websites	O
on	O
the	O
Internet	O
.	O
</s>
<s>
It	O
was	O
first	O
introduced	O
in	O
1997	O
as	O
a	O
means	O
to	O
block	O
spam	O
email	O
from	O
known	O
malicious	O
IP	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
DNS	B-Application
blocking	I-Application
can	O
also	O
be	O
applied	O
for	O
outgoing	O
requests	O
as	O
well	O
.	O
</s>
<s>
Instead	O
of	O
returning	O
the	O
valid	O
IP	B-Protocol
address	I-Protocol
of	O
a	O
requested	O
site	O
(	O
for	O
example	O
,	O
instead	O
of	O
198.35.26.96	O
being	O
returned	O
by	O
the	O
DNS	B-Protocol
when	O
"	O
www.wikipedia.org	O
"	O
is	O
entered	O
into	O
a	O
browser	O
,	O
if	O
this	O
IP	O
were	O
on	O
a	O
block	O
list	O
,	O
the	O
DNS	B-Protocol
might	O
reply	O
that	O
the	O
domain	O
is	O
unknown	O
or	O
with	O
a	O
different	O
IP	B-Protocol
address	I-Protocol
that	O
directs	O
to	O
a	O
site	O
with	O
a	O
page	O
stating	O
that	O
the	O
requested	O
domain	O
is	O
not	O
permitted	O
)	O
.	O
</s>
<s>
The	O
latter	O
case	O
where	O
the	O
user	O
is	O
redirected	O
to	O
another	O
destination	O
would	O
be	O
considered	O
DNS	B-Protocol
Spoofing	O
,	O
otherwise	O
known	O
as	O
"	O
DNS	B-Protocol
Poisoning	O
"	O
.	O
</s>
<s>
DNS	B-Application
blocking	I-Application
can	O
be	O
applied	O
to	O
individual	O
servers/IP	O
address	O
,	O
or	O
entire	O
blocks	O
of	O
IP	B-Protocol
addresses	I-Protocol
for	O
multiple	O
reasons	O
.	O
</s>
<s>
Some	O
public	O
DNS	B-Protocol
Resolvers	O
,	O
like	O
Quad9	B-Protocol
and	O
CleanBrowsing	B-Protocol
offer	O
filters	O
are	O
part	O
of	O
their	O
DNS	B-Protocol
.	O
</s>
<s>
Quad9	B-Protocol
,	O
for	O
example	O
,	O
blocks	O
access	O
to	O
known	O
phishing	O
and	O
malicious	O
domains	O
.	O
</s>
<s>
CleanBrowsing	B-Protocol
filters	O
out	O
adult	O
content	O
in	O
their	O
effort	O
to	O
protect	O
kids	O
online	O
.	O
</s>
<s>
In	O
addition	O
to	O
its	O
technical	O
impact	O
,	O
DNS	B-Application
blocking	I-Application
also	O
has	O
many	O
social	O
and	O
political	O
implications	O
.	O
</s>
<s>
Free	O
speech	O
and	O
due	O
process	O
are	O
key	O
concerns	O
regarding	O
DNS	B-Application
blocking	I-Application
,	O
particularly	O
in	O
the	O
United	O
States	O
.	O
</s>
<s>
DNS	B-Application
blocking	I-Application
was	O
proposed	O
to	O
be	O
mandated	O
by	O
the	O
Stop	B-Application
Online	I-Application
Piracy	I-Application
Act	I-Application
(	O
SOPA	B-Application
)	O
and	O
the	O
PROTECT	O
IP	O
Act	O
(	O
PIPA	O
)	O
.	O
</s>
<s>
The	O
goal	O
for	O
its	O
use	O
as	O
intended	O
by	O
SOPA	B-Application
and	O
PIPA	O
is	O
to	O
prevent	O
users	O
from	O
intentionally	O
or	O
unintentionally	O
accessing	O
web	O
sites	O
and	O
web	O
services	O
that	O
are	O
known	O
to	O
host	O
copyrighted	O
material	O
without	O
authorization	O
.	O
</s>
<s>
According	O
to	O
an	O
article	O
in	O
Network	O
World	O
magazine	O
,	O
"	O
Just	O
about	O
universally	O
,	O
the	O
people	O
responsible	O
for	O
the	O
technical	O
development	O
and	O
operation	O
of	O
the	O
Internet	O
have	O
said	O
that	O
the	O
DNS-blocking	O
proposals	O
would	O
break	O
vital	O
Internet	O
technology	O
while	O
at	O
the	O
same	O
time	O
being	O
entirely	O
ineffectual	O
against	O
people	O
who	O
are	O
serious	O
about	O
violating	O
copyright	O
laws	O
and	O
largely	O
ineffectual	O
against	O
those	O
who	O
do	O
so	O
casually.	O
"	O
</s>
<s>
Google	B-Application
's	I-Application
chairman	O
,	O
Eric	O
Schmidt	O
,	O
is	O
quoted	O
saying	O
"	O
I	O
would	O
be	O
very	O
,	O
very	O
careful	O
if	O
I	O
were	O
a	O
government	O
about	O
arbitrarily	O
 [ implementing ] 	O
simple	O
solutions	O
to	O
complex	O
problems	O
"	O
in	O
reference	O
to	O
DNS	B-Application
blocking	I-Application
and	O
the	O
PIPA	O
bill	O
.	O
</s>
<s>
Experts	O
claim	O
that	O
users	O
could	O
get	O
around	O
DNS	B-Application
blocking	I-Application
by	O
using	O
foreign	O
search	O
engines	O
and	O
foreign	O
DNS	B-Protocol
servers	O
.	O
</s>
<s>
Numerous	O
industry	O
experts	O
have	O
concerns	O
regarding	O
the	O
effect	O
of	O
DNS	B-Application
blocking	I-Application
on	O
the	O
security	O
of	O
the	O
Internet	O
.	O
</s>
<s>
A	O
former	O
Bush	O
administration	O
Department	O
of	O
Homeland	O
Security	O
policy	O
director	O
claimed	O
that	O
altering	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
"	O
would	O
do	O
great	O
damage	O
to	O
internet	O
security.	O
"	O
</s>
