<s>
An	O
open	B-Protocol
proxy	I-Protocol
is	O
a	O
type	O
of	O
proxy	B-Application
server	I-Application
that	O
is	O
accessible	O
by	O
any	O
Internet	O
user	O
.	O
</s>
<s>
Generally	O
,	O
a	O
proxy	B-Application
server	I-Application
only	O
allows	O
users	O
within	O
a	O
network	O
group	O
(	O
i.e.	O
</s>
<s>
a	O
closed	B-Protocol
proxy	I-Protocol
)	O
to	O
store	B-Protocol
and	I-Protocol
forward	I-Protocol
Internet	O
services	O
such	O
as	O
DNS	B-Protocol
or	O
web	O
pages	O
to	O
reduce	O
and	O
control	O
the	O
bandwidth	O
used	O
by	O
the	O
group	O
.	O
</s>
<s>
With	O
an	O
open	B-Protocol
proxy	I-Protocol
,	O
however	O
,	O
any	O
user	O
on	O
the	O
Internet	O
is	O
able	O
to	O
use	O
this	O
forwarding	O
service	O
.	O
</s>
<s>
An	O
anonymous	O
open	B-Protocol
proxy	I-Protocol
is	O
useful	O
to	O
those	O
looking	O
for	O
online	O
anonymity	O
and	O
privacy	O
,	O
as	O
it	O
can	O
help	O
users	O
hide	O
their	O
IP	B-Protocol
address	I-Protocol
from	O
web	O
servers	O
since	O
the	O
server	O
requests	O
appear	O
to	O
originate	O
from	O
the	O
proxy	B-Application
server	I-Application
.	O
</s>
<s>
Real	O
anonymity	O
and	O
extensive	O
internet	B-Application
security	I-Application
might	O
not	O
be	O
achieved	O
by	O
this	O
measure	O
alone	O
as	O
website	O
operators	O
can	O
use	O
client-side	O
scripts	O
to	O
determine	O
the	O
browser	O
's	O
real	O
IP	B-Protocol
address	I-Protocol
and	O
the	O
open	B-Protocol
proxy	I-Protocol
may	O
be	O
keeping	O
logs	O
of	O
all	O
connections	O
.	O
</s>
<s>
Open	B-Protocol
proxies	I-Protocol
also	O
do	O
n't	O
stop	O
tracking	O
cookies	O
and	O
fingerprinters	B-Protocol
from	O
identifying	O
users	O
.	O
</s>
<s>
Most	O
public	O
VPNs	B-Application
work	O
through	O
open	B-Protocol
proxies	I-Protocol
.	O
</s>
<s>
It	O
is	O
possible	O
for	O
a	O
computer	O
to	O
run	O
as	O
an	O
open	B-Protocol
proxy	I-Protocol
server	I-Protocol
without	O
the	O
computer	O
's	O
owner	O
knowing	O
it	O
.	O
</s>
<s>
Because	O
open	B-Protocol
proxies	I-Protocol
are	O
often	O
implicated	O
in	O
abuse	O
,	O
a	O
number	O
of	O
methods	O
have	O
been	O
developed	O
to	O
detect	O
them	O
and	O
to	O
refuse	O
service	O
to	O
them	O
.	O
</s>
<s>
IRC	B-Protocol
networks	I-Protocol
with	O
strict	O
usage	O
policies	O
automatically	O
test	O
client	O
systems	O
for	O
known	O
types	O
of	O
open	B-Protocol
proxies	I-Protocol
.	O
</s>
<s>
Likewise	O
,	O
a	O
mail	B-Protocol
server	I-Protocol
may	O
be	O
configured	O
to	O
automatically	O
test	O
mail	O
senders	O
for	O
open	B-Protocol
proxies	I-Protocol
,	O
using	O
software	O
such	O
as	O
proxycheck	O
.	O
</s>
<s>
Groups	O
of	O
IRC	B-Protocol
and	O
electronic	O
mail	O
operators	O
run	O
DNSBLs	O
publishing	O
lists	O
of	O
the	O
IP	B-Protocol
addresses	I-Protocol
of	O
known	O
open	B-Protocol
proxies	I-Protocol
,	O
such	O
as	O
AHBL	O
,	O
CBL	O
,	O
NJABL	O
(	O
till	O
2013	O
)	O
,	O
and	O
SORBS	O
(	O
in	O
operation	O
since	O
2002	O
)	O
.	O
</s>
