<s>
Control	B-Protocol
messages	I-Protocol
are	O
a	O
special	O
kind	O
of	O
Usenet	B-Application
post	O
that	O
are	O
used	O
to	O
control	O
news	B-Application
servers	I-Application
.	O
</s>
<s>
However	O
,	O
the	O
traditional	O
format	O
of	O
the	O
subject	O
line	O
is	O
widely	O
used	O
in	O
addition	O
to	O
the	O
Control	O
header	O
:	O
the	O
subject	O
line	O
consists	O
of	O
the	O
word	O
"	O
cmsg	B-Protocol
"	O
followed	O
by	O
control	O
name	O
and	O
arguments	O
.	O
</s>
<s>
This	O
verification	O
does	O
not	O
work	O
well	O
in	O
modern	O
day	O
Usenet	B-Application
and	O
is	O
rarely	O
used	O
.	O
</s>
<s>
Additional	O
hierarchy	O
specific	O
rules	O
(	O
see	O
Breidbart	O
Index	O
)	O
allow	O
cancelbots	B-Protocol
to	O
send	O
third-party	O
cancels	O
to	O
remove	O
spam	O
.	O
</s>
<s>
A	O
newgroup	B-Protocol
message	O
is	O
issued	O
to	O
create	O
a	O
new	O
Usenet	B-Application
newsgroup	I-Application
.	O
</s>
<s>
Typically	O
newgroup	B-Protocol
messages	O
having	O
a	O
correct	O
digital	O
signature	O
are	O
executed	O
automatically	O
.	O
</s>
<s>
In	O
some	O
hierarchies	O
(	O
,	O
,	O
)	O
unsigned	O
newgroup	B-Protocol
messages	O
just	O
serve	O
as	O
formalized	O
proposal	O
to	O
create	O
a	O
new	O
group	O
.	O
</s>
<s>
In	O
many	O
cases	O
newgroup	B-Protocol
messages	O
are	O
archived	O
by	O
the	O
Internet	O
Systems	O
Consortium	O
.	O
</s>
<s>
A	O
rmgroup	O
message	O
is	O
issued	O
to	O
remove	O
a	O
newsgroup	B-Application
.	O
</s>
<s>
In	O
some	O
hierarchies	O
unsigned	O
rmgroup	O
messages	O
are	O
used	O
to	O
veto	O
a	O
preceding	O
newgroup	B-Protocol
.	O
</s>
<s>
Objections	O
to	O
the	O
proposal	O
are	O
then	O
expressed	O
with	O
a	O
newgroup	B-Protocol
.	O
</s>
<s>
In	O
1995	O
the	O
Church	O
of	O
Scientology	O
attempted	O
to	O
silence	O
criticism	O
by	O
sending	O
mass	O
"	O
rmgroup	O
"	O
messages	O
to	O
Usenet	B-Application
servers	O
targeting	O
alt.religion.scientology	B-Application
,	O
an	O
example	O
of	O
the	O
church	O
's	O
continuing	B-Application
efforts	I-Application
to	O
suppress	O
material	O
critical	O
of	O
Scientology	O
on	O
the	O
Internet	O
.	O
</s>
<s>
Most	O
servers	O
discarded	O
the	O
message	O
,	O
and	O
those	O
that	O
did	O
not	O
were	O
quickly	O
sent	O
"	O
newgroup	B-Protocol
"	O
messages	O
reestablishing	O
the	O
newsgroup	B-Application
.	O
</s>
<s>
The	O
ihave/sendme	O
protocol	O
was	O
obsoleted	O
by	O
NNTP	B-Protocol
.	O
</s>
<s>
Answering	O
control	B-Protocol
messages	I-Protocol
with	O
large	O
emails	O
can	O
be	O
exploited	O
for	O
a	O
Denial	O
of	O
service	O
attack	O
.	O
</s>
<s>
Thus	O
news	B-Application
servers	I-Application
stopped	O
implementing	O
long	O
before	O
it	O
was	O
declared	O
obsolete	O
by	O
RFC	O
5537	O
.	O
</s>
<s>
Newsservers	B-Application
traditionally	O
allow	O
only	O
selected	O
users	O
to	O
send	O
articles	O
with	O
these	O
lines	O
.	O
</s>
<s>
As	O
long	O
as	O
there	O
were	O
only	O
a	O
handful	O
of	O
Usenet	B-Application
sites	O
this	O
provided	O
sufficient	O
protection	O
against	O
abuse	O
.	O
</s>
<s>
The	O
format	O
of	O
"	O
Arpa	O
Internet	O
Text	O
Messages	O
"	O
is	O
the	O
common	O
base	O
for	O
Usenet	B-Application
and	O
E-mail	O
.	O
</s>
<s>
For	O
control	B-Protocol
message	I-Protocol
a	O
special	O
format	O
is	O
required	O
since	O
the	O
essential	O
information	O
is	O
in	O
the	O
header	O
fields	O
.	O
</s>
<s>
Pgpcontrol	O
was	O
originally	O
designed	O
for	O
PGP	B-Application
but	O
also	O
works	O
with	O
OpenPGP	O
.	O
</s>
<s>
Newsgroup	B-Application
maintenance	O
of	O
the	O
main	O
Usenet	B-Application
hierarchies	O
(	O
Big	B-Architecture
8	I-Architecture
and	O
regional	O
hierarchies	O
)	O
is	O
done	O
through	O
signed	O
control	B-Protocol
messages	I-Protocol
.	O
</s>
<s>
Most	O
newsservers	B-Application
are	O
configured	O
to	O
both	O
automatically	O
execute	O
controls	O
signed	O
with	O
the	O
right	O
key	O
and	O
ignore	O
anything	O
else	O
.	O
</s>
<s>
However	O
,	O
it	O
would	O
not	O
only	O
require	O
a	O
key	O
pair	O
for	O
every	O
Usenet	B-Application
user	O
but	O
also	O
that	O
the	O
respective	O
public	O
key	O
is	O
known	O
to	O
every	O
news	B-Application
server	I-Application
.	O
</s>
<s>
Cancel-lock	O
is	O
much	O
simpler	O
,	O
but	O
neither	O
commonly	O
accepted	O
,	O
nor	O
implemented	O
in	O
popular	O
news	B-Application
servers	I-Application
and	O
newsreaders	B-Protocol
.	O
</s>
<s>
Control	B-Protocol
messages	I-Protocol
are	O
typically	O
not	O
shown	O
in	O
the	O
target	O
newsgroup	B-Application
.	O
</s>
<s>
Instead	O
many	O
servers	O
put	O
them	O
into	O
pseudo	O
newsgroups	B-Application
like	O
control	O
.	O
</s>
<s>
Google	B-Application
Groups	I-Application
provides	O
no	O
means	O
to	O
read	O
or	O
write	O
control	B-Protocol
messages	I-Protocol
.	O
</s>
