<s>
The	O
child	B-Application
abuse	I-Application
image	I-Application
content	I-Application
list	I-Application
(	O
CAIC	B-Application
List	I-Application
)	O
is	O
a	O
list	O
of	O
URLs	O
and	O
image	B-Application
hashes	I-Application
provided	O
by	O
the	O
Internet	O
Watch	O
Foundation	O
to	O
its	O
partners	O
to	O
enable	O
the	O
blocking	O
of	O
child	O
pornography	O
&	O
criminally	O
obscene	O
adult	O
content	O
in	O
the	O
UK	O
and	O
by	O
major	O
international	O
technology	O
companies	O
.	O
</s>
<s>
Cleanfeed	O
was	O
temporarily	O
extended	O
to	O
block	O
Newzbin	B-Application
until	O
this	O
process	O
was	O
moved	O
to	O
ISP-specific	O
programmes	O
.	O
</s>
<s>
Cleanfeed	O
is	O
a	O
content	B-Protocol
blocking	I-Protocol
system	I-Protocol
technology	O
implemented	O
in	O
the	O
UK	O
by	O
BT	O
,	O
Britain	O
's	O
largest	O
Internet	O
provider	O
.	O
</s>
<s>
Cleanfeed	O
is	O
a	O
silent	O
content	B-Protocol
filtering	I-Protocol
system	O
,	O
which	O
means	O
that	O
Internet	O
users	O
cannot	O
ascertain	O
whether	O
they	O
are	O
being	O
regulated	O
by	O
Cleanfeed	O
,	O
facing	O
connection	O
failures	O
,	O
or	O
the	O
page	O
really	O
does	O
not	O
exist	O
.	O
</s>
<s>
In	O
June	O
2011	O
the	O
Motion	O
Picture	O
Association	O
began	O
court	O
proceedings	O
in	O
an	O
attempt	O
to	O
force	O
BT	O
to	O
use	O
Cleanfeed	O
to	O
block	O
access	O
to	O
NewzBin2	B-Application
,	O
a	O
site	O
indexing	O
downloads	O
of	O
copyrighted	O
content	O
.	O
</s>
<s>
The	O
case	O
(	O
Twentieth	O
Century	O
Fox	O
Film	O
Corp	O
&	O
Ors	O
v	O
British	O
Telecommunications	O
Plc	O
 [ 2011 ] 	O
)	O
only	O
compels	O
BT	O
's	O
ISP	O
division	O
to	O
implement	O
the	O
block	O
on	O
NewzBin	B-Application
,	O
it	O
remains	O
outside	O
of	O
remit	O
of	O
the	O
IWF	O
URL	O
list	O
which	O
is	O
strictly	O
limited	O
to	O
blocking	O
sites	O
which	O
host	O
child	O
sexual	O
abuse	O
content	O
.	O
</s>
<s>
In	O
August	O
2015	O
the	O
IWF	O
announced	O
it	O
was	O
to	O
begin	O
sharing	O
the	O
list	O
with	O
tech	O
giants	O
Facebook	B-Application
,	O
Google	B-Application
,	O
Twitter	B-Application
and	O
Yahoo	B-Application
to	O
block	O
contents	O
being	O
distributed	O
through	O
their	O
networks	O
.	O
</s>
<s>
Routers	B-Protocol
on	O
the	O
edge	O
redirect	O
traffic	O
to	O
these	O
sites	O
to	O
special	O
HTTP	B-Protocol
proxy	B-Application
servers	I-Application
which	O
perform	O
the	O
actual	O
filtering	O
by	O
matching	O
HTTP	B-Protocol
requests	I-Protocol
to	O
URLs	O
on	O
the	O
blacklist	O
.	O
</s>
<s>
The	O
routers	B-Protocol
at	O
an	O
ISP	O
that	O
has	O
implemented	O
Cleanfeed	O
technology	O
check	O
traffic	O
destination	O
against	O
a	O
list	O
of	O
IP	B-Protocol
addresses	I-Protocol
of	O
sites	O
that	O
are	O
suspected	O
of	O
hosting	O
filtered	O
traffic	O
.	O
</s>
<s>
If	O
the	O
site	O
IP	B-Protocol
address	I-Protocol
is	O
found	O
in	O
the	O
list	O
of	O
suspected	O
sources	O
of	O
unwanted	O
material	O
,	O
the	O
traffic	O
is	O
routed	O
to	O
proxies	O
(	O
highlighted	O
as	O
IWF	O
proxies	O
)	O
that	O
check	O
the	O
specific	O
page	O
against	O
a	O
confidential	O
blacklist	O
of	O
pages	O
.	O
</s>
<s>
This	O
two-pass	O
implementation	O
reduces	O
the	O
load	O
on	O
the	O
proxy	B-Application
servers	I-Application
by	O
not	O
requiring	O
that	O
all	O
traffic	O
pass	O
through	O
them	O
.	O
</s>
<s>
In	O
the	O
example	O
below	O
,	O
the	O
IP	B-Protocol
addresses	I-Protocol
in	O
bold	O
are	O
the	O
ISP	O
filtering	O
servers	O
.	O
</s>
<s>
Demon	O
Internet	O
were	O
the	O
only	O
ISP	O
to	O
notify	O
users	O
routinely	O
when	O
content	O
is	O
blocked	O
and	O
offer	O
the	O
option	O
to	O
intercept	O
and	O
serve	O
filtered	O
content	O
over	O
https	B-Protocol
connections	O
.	O
</s>
<s>
The	O
other	O
popular	O
way	O
of	O
blocking	O
content	O
is	O
DNS	B-Protocol
manipulation	O
.	O
</s>
<s>
Slightly	O
harder	O
to	O
circumvent	O
,	O
although	O
users	O
can	O
use	O
open	B-Protocol
proxies	I-Protocol
,	O
or	O
the	O
Tor	B-Application
network	I-Application
,	O
and	O
servers	O
can	O
use	O
another	O
port	O
than	O
80	O
,	O
or	O
HTTPS	B-Protocol
.	O
</s>
<s>
DNS-based	O
blocking	O
is	O
criticized	O
for	O
blocking	O
all	O
content	O
on	O
a	O
site	O
with	O
the	O
same	O
domain	O
name	O
.	O
</s>
<s>
DNS-based	O
schemes	O
also	O
break	O
the	O
whole	O
concept	O
of	O
DNS	B-Protocol
security	I-Protocol
.	O
</s>
<s>
60.87	O
%	O
did	O
not	O
trust	O
BT	O
,	O
and	O
65.22	O
%	O
did	O
not	O
trust	O
IWF	O
to	O
be	O
responsible	O
for	O
a	O
silent	O
content	B-Protocol
blocking	I-Protocol
system	I-Protocol
in	O
the	O
UK	O
.	O
</s>
<s>
A	O
majority	O
of	O
the	O
participants	O
preferred	O
an	O
open	O
content	B-Protocol
blocking	I-Protocol
system	I-Protocol
targeting	O
child	O
abuse	O
content	O
,	O
rather	O
than	O
no	O
Internet	O
regulation	O
.	O
</s>
<s>
Another	O
criticism	O
is	O
that	O
Newzbin	B-Application
claims	O
to	O
have	O
successfully	O
circumvented	O
Cleanfeed	O
following	O
a	O
court	O
order	O
forcing	O
BT	O
to	O
censor	O
the	O
website	O
over	O
copyright	O
infringement	O
claims	O
.	O
</s>
<s>
Due	O
to	O
the	O
proxy	B-Application
server	I-Application
implementation	O
of	O
the	O
Cleanfeed	O
system	O
,	O
websites	O
that	O
filter	O
users	O
by	O
IP	B-Protocol
address	I-Protocol
such	O
as	O
wikis	B-Protocol
and	O
file	B-Application
lockers	I-Application
will	O
be	O
significantly	O
broken	O
through	O
the	O
system	O
,	O
even	O
if	O
only	O
a	O
tiny	O
proportion	O
of	O
its	O
content	O
is	O
blocked	O
.	O
</s>
