<s>
CTX	B-Application
is	O
a	O
computer	O
virus	O
created	O
in	O
Spain	O
in	O
1999	O
.	O
</s>
<s>
CTX	B-Application
was	O
initially	O
discovered	O
as	O
part	O
of	O
the	O
Cholera	O
worm	O
,	O
with	O
which	O
the	O
author	O
intentionally	O
infected	O
with	O
CTX	B-Application
.	O
</s>
<s>
Although	O
the	O
Cholera	O
worm	O
had	O
the	O
capability	O
to	O
send	O
itself	O
via	O
email	O
,	O
the	O
CTX	B-Application
worm	O
quickly	O
surpassed	O
it	O
in	O
prevalence	O
.	O
</s>
<s>
Cholera	O
is	O
now	O
considered	O
obsolete	O
,	O
while	O
CTX	B-Application
remains	O
in	O
the	O
field	O
,	O
albeit	O
with	O
only	O
rare	O
discoveries	O
.	O
</s>
<s>
In	O
March	O
2006	O
,	O
CTX	B-Application
was	O
in	O
the	O
news	O
again	O
due	O
to	O
a	O
false	O
positive	O
in	O
the	O
McAfee	B-Operating_System
VirusScan	I-Operating_System
program	O
that	O
caused	O
CTX	B-Application
detections	O
in	O
a	O
range	O
of	O
innocuous	O
files	O
.	O
</s>
<s>
The	O
CTX	B-Application
virus	O
originated	O
as	O
part	O
of	O
the	O
"	O
Simbiosis	O
(	O
sic	O
)	O
Project	O
"	O
.	O
</s>
<s>
The	O
Simbiosis	O
Project	O
was	O
an	O
early	O
attempt	O
by	O
the	O
29A	O
virus	O
writers	O
group	O
to	O
combine	O
Windows	B-Application
file	O
infectors	O
with	O
Windows	B-Application
mass-mailing	O
worms	O
.	O
</s>
<s>
Cholera/CTX	O
is	O
the	O
only	O
documented	O
virus	O
involved	O
in	O
the	O
Simbiosis	O
Project	O
.	O
</s>
<s>
Although	O
CTX	B-Application
did	O
gain	O
some	O
spread	O
in	O
the	O
wild	O
,	O
this	O
was	O
remarkably	O
more	O
related	O
to	O
its	O
file	O
infection	O
functions	O
than	O
the	O
Cholera	O
mass-mailing	O
function	O
.	O
</s>
<s>
CTX	B-Application
was	O
also	O
a	O
member	O
of	O
the	O
"	O
BioCoded	O
"	O
string	O
of	O
viruses	O
.	O
</s>
<s>
All	O
"	O
BioCoded	O
"	O
viruses	O
have	O
been	O
listed	O
on	O
the	O
,	O
including	O
CTX	B-Application
.	O
</s>
<s>
Despite	O
their	O
threatening	O
names	O
,	O
CTX	B-Application
and	O
all	O
BioCoded	O
viruses	O
have	O
no	O
payload	O
beyond	O
graphics	O
and	O
,	O
in	O
some	O
cases	O
,	O
deleting	O
antivirus	O
programs	O
.	O
</s>
<s>
By	O
today	O
's	O
standards	O
,	O
Cholera	O
is	O
a	O
fairly	O
unremarkable	O
mass-mailing	O
worm	O
,	O
written	O
in	O
C++	B-Language
.	O
</s>
<s>
However	O
,	O
Cholera	O
was	O
remarkable	O
at	O
its	O
creation	O
for	O
its	O
use	O
of	O
its	O
own	O
SMTP	B-Protocol
server	I-Protocol
.	O
</s>
<s>
Unlike	O
most	O
worms	O
of	O
the	O
day	O
,	O
which	O
relied	O
on	O
installations	O
of	O
Microsoft	B-Application
Outlook	I-Application
or	O
similar	O
email	O
programs	O
,	O
Cholera	O
was	O
capable	O
of	O
sending	O
its	O
own	O
mails	O
through	O
internal	O
mechanisms	O
.	O
</s>
<s>
Cholera	O
only	O
spreads	O
when	O
another	O
Internet-using	O
application	O
is	O
open	O
,	O
to	O
avoid	O
detection	O
in	O
a	O
time	O
when	O
dial-up	B-Application
modems	I-Application
were	O
standard	O
.	O
</s>
<s>
Cholera	O
is	O
also	O
a	O
network	O
worm	O
,	O
inserting	O
itself	O
into	O
the	O
Windows	B-Application
folders	O
of	O
computers	O
available	O
through	O
Network	B-Protocol
Neighborhood	I-Protocol
.	O
</s>
<s>
Finally	O
,	O
Cholera	O
will	O
add	O
itself	O
to	O
either	O
WIN.INI	B-Protocol
(	O
Windows	B-Application
95	I-Application
and	O
similar	O
flavours	O
)	O
or	O
the	O
Registry	B-Protocol
(	O
Windows	B-Device
NT	I-Device
and	O
similar	O
flavours	O
)	O
.	O
</s>
<s>
Upon	O
execution	O
,	O
whether	O
from	O
an	O
infected	O
file	O
or	O
the	O
Cholera	O
dropper	O
,	O
CTX	B-Application
will	O
check	O
to	O
see	O
if	O
its	O
payload	O
routine	O
should	O
activate	O
(	O
see	O
Payload	O
)	O
.	O
</s>
<s>
If	O
not	O
,	O
CTX	B-Application
will	O
infect	O
EXE	O
files	O
.	O
</s>
<s>
CTX	B-Application
has	O
a	O
polymorphic	O
nature	O
,	O
which	O
is	O
neither	O
particularly	O
simple	O
or	O
complex	O
in	O
nature	O
.	O
</s>
<s>
CTX	B-Application
also	O
obscures	O
the	O
entry	B-Language
point	I-Language
of	O
files	O
to	O
avoid	O
detection	O
.	O
</s>
<s>
Files	O
infecting	O
with	O
CTX	B-Application
are	O
padded	O
to	O
a	O
multiple	O
of	O
101	O
bytes	O
to	O
avoid	O
re-infections	O
.	O
</s>
<s>
CTX	B-Application
has	O
a	O
non-destructive	O
payload	O
which	O
rarely	O
activates	O
.	O
</s>
<s>
If	O
a	O
file	O
is	O
executed	O
exactly	O
six	O
months	O
to	O
the	O
hour	O
after	O
infection	O
,	O
and	O
the	O
video	O
requirements	O
are	O
sufficient	O
,	O
CTX	B-Application
will	O
go	O
into	O
an	O
infinite	O
loop	O
of	O
inverting	O
the	O
desktop	O
colours	O
.	O
</s>
<s>
The	O
,	O
an	O
organization	O
tracking	O
computer	O
viruses	O
,	O
included	O
CTX	B-Application
on	O
its	O
list	O
of	O
threats	O
found	O
in	O
the	O
field	O
from	O
November	O
2001	O
to	O
May	O
2005	O
.	O
</s>
<s>
On	O
17	O
March	O
2006	O
,	O
McAfee	O
,	O
makers	O
of	O
VirusScan	B-Operating_System
,	O
announced	O
that	O
a	O
false	O
positive	O
had	O
caused	O
the	O
CTX	B-Application
virus	O
to	O
be	O
detected	O
in	O
a	O
number	O
of	O
common	O
,	O
innocent	O
files	O
,	O
including	O
Microsoft	B-Application
Excel	I-Application
.	O
</s>
