<s>
ABC	B-Application
,	O
discovered	O
in	O
October	O
1992	O
,	O
is	O
a	O
memory-resident	O
,	O
file-infecting	O
computer	O
virus	O
which	O
infects	O
EXE	O
files	O
and	O
may	O
alter	O
both	O
COM	O
and	O
EXE	O
files	O
.	O
</s>
<s>
ABC	B-Application
activates	O
on	O
the	O
13th	B-Device
day	I-Device
of	O
every	O
month	O
.	O
</s>
<s>
Upon	O
infection	O
,	O
ABC	B-Application
becomes	O
memory-resident	O
at	O
the	O
top	O
of	O
system	O
memory	O
but	O
below	O
the	O
640K	O
DOS	B-Device
boundary	O
and	O
hooks	O
interrupts	B-Application
16	O
and	O
1C	O
.	O
</s>
<s>
The	O
copy	O
of	O
command.com	B-Operating_System
pointed	O
to	O
by	O
the	O
COMSPEC	O
environment	O
variable	O
may	O
also	O
be	O
altered	O
.	O
</s>
<s>
ABC	B-Application
infects/alters	O
COM	O
and	O
EXE	O
files	O
as	O
they	O
are	O
executed	O
.	O
</s>
<s>
After	O
infection	O
,	O
total	O
system	O
memory	O
,	O
as	O
measured	O
by	O
the	O
DOS	B-Device
CHKDSK	B-Device
program	O
,	O
will	O
not	O
be	O
altered	O
,	O
but	O
available	O
free	O
memory	O
will	O
have	O
decreased	O
by	O
approximately	O
8,960	O
bytes	B-Application
.	O
</s>
<s>
Altered	O
,	O
but	O
not	O
infected	O
,	O
COM	O
or	O
EXE	O
files	O
will	O
have	O
4	O
to	O
30	O
bytes	B-Application
added	O
to	O
their	O
length	O
.	O
</s>
<s>
Infected	O
EXE	O
files	O
(	O
COM	O
files	O
are	O
never	O
infected	O
)	O
have	O
a	O
file	O
length	O
increase	O
of	O
2,952	O
to	O
2,972	O
bytes	B-Application
,	O
and	O
ABC	B-Application
is	O
located	O
at	O
the	O
end	O
of	O
the	O
infected	O
EXE	O
.	O
</s>
<s>
An	O
altered/infected	O
file	O
's	O
date	O
and	O
time	O
in	O
the	O
DOS	B-Device
disk	O
directory	O
listing	O
may	O
have	O
been	O
updated	O
to	O
the	O
current	O
system	O
date	O
and	O
time	O
when	O
the	O
file	O
was	O
altered/infected	O
.	O
</s>
<s>
No	O
text	O
strings	O
are	O
visible	O
within	O
the	O
viral	O
code	O
in	O
infected	O
EXE	O
files	O
,	O
but	O
the	O
following	O
text	O
strings	O
are	O
encrypted	O
within	O
the	O
initial	O
copy	O
of	O
the	O
ABC	B-Application
virus	I-Application
:	O
</s>
<s>
ABC	B-Application
causes	O
keystrokes	O
on	O
the	O
compromised	O
machine	O
to	O
be	O
repeated	O
.	O
</s>
<s>
System	O
hangs	O
may	O
also	O
occur	O
when	O
some	O
programs	O
are	O
executed	O
,	O
a	O
likely	O
side	O
effect	O
of	O
ABC-induced	O
corruption	O
.	O
</s>
<s>
The	O
ABC	B-Application
virus	I-Application
is	O
not	O
to	O
be	O
confused	O
with	O
the	O
ABC	B-Application
keylogger	O
trojan	O
,	O
written	O
in	O
2004	O
by	O
Jan	O
ten	O
Hove	O
.	O
</s>
