<s>
AIDS	B-Application
is	O
a	O
DOS	B-Device
computer	O
virus	O
which	O
overwrites	O
COM	O
files	O
.	O
</s>
<s>
AIDS	B-Application
is	O
the	O
first	O
virus	O
known	O
to	O
exploit	O
the	O
MS-DOS	B-Application
"	O
corresponding	O
file	O
"	O
vulnerability	O
.	O
</s>
<s>
In	O
MS-DOS	B-Application
,	O
if	O
the	O
user	O
enters	O
in	O
the	O
command	O
interpreter	O
,	O
in	O
a	O
directory	O
where	O
both	O
and	O
exist	O
,	O
then	O
will	O
always	O
be	O
executed	O
.	O
</s>
<s>
Thus	O
,	O
by	O
creating	O
infected	O
COM	O
files	O
,	O
AIDS	B-Application
code	O
will	O
always	O
be	O
executed	O
before	O
the	O
intended	O
EXE	O
file	O
.	O
</s>
<s>
When	O
the	O
AIDS	B-Application
virus	O
activates	O
,	O
it	O
displays	O
the	O
following	O
screen	O
:	O
</s>
<s>
ATTENTION	O
:	O
I	O
have	O
been	O
elected	O
to	O
inform	O
you	O
that	O
throughout	O
your	O
process	O
of	O
collecting	O
and	O
executing	O
files	O
,	O
you	O
have	O
accidentally	O
¶HÜ¢KΣ►	O
[	O
phucked	O
in	O
leet ]	O
yourself	O
over	O
:	O
again	O
,	O
that	O
's	O
PHUCKED	O
yourself	O
over	O
.	O
</s>
<s>
In	O
the	O
message	O
above	O
,	O
the	O
word	O
"	O
AIDS	B-Application
"	O
covers	O
about	O
half	O
of	O
the	O
screen	O
.	O
</s>
<s>
The	O
AIDS	B-Application
virus	O
overwrites	O
the	O
first	O
13,952	O
bytes	B-Application
of	O
an	O
infected	O
COM	O
file	O
.	O
</s>
<s>
AIDS	B-Application
II	I-Application
is	O
a	O
companion	O
computer	O
virus	O
,	O
which	O
infects	O
COM	O
files	O
.	O
</s>
<s>
First	O
discovered	O
in	O
April	O
1990	O
,	O
it	O
appears	O
to	O
be	O
a	O
more	O
elegant	O
revision	O
of	O
AIDS	B-Application
,	O
which	O
also	O
employs	O
the	O
corresponding	O
file	O
technique	O
to	O
execute	O
infected	O
code	O
.	O
</s>
<s>
Unlike	O
generic	O
file	O
infectors	O
,	O
AIDS	B-Application
II	I-Application
is	O
the	O
second	O
known	O
virus	O
to	O
use	O
the	O
"	O
corresponding	O
file	O
technique	O
"	O
of	O
infection	O
(	O
after	O
the	O
original	O
AIDS	B-Application
)	O
,	O
and	O
the	O
first	O
to	O
use	O
this	O
technique	O
in	O
a	O
way	O
that	O
does	O
not	O
modify	O
the	O
original	O
target	O
EXE	O
file	O
.	O
</s>
<s>
AIDS	B-Application
II	I-Application
works	O
by	O
first	O
finding	O
an	O
uninfected	O
EXE	O
file	O
in	O
the	O
working	B-Application
directory	I-Application
and	O
then	O
creating	O
a	O
companion	O
COM	O
file	O
with	O
the	O
viral	O
code	O
.	O
</s>
<s>
The	O
COM	O
files	O
will	O
always	O
be	O
8,064	O
bytes	B-Application
in	O
length	O
,	O
with	O
a	O
timestamp	O
corresponding	O
to	O
the	O
time	O
of	O
infection	O
.	O
</s>
<s>
AIDS	B-Application
II	I-Application
then	O
executes	O
EXE	O
file	O
the	O
user	O
intended	O
to	O
execute	O
without	O
incident	O
.	O
</s>
<s>
Since	O
the	O
EXE	O
file	O
is	O
unchanged	O
,	O
cyclic	O
redundancy	O
checks	O
,	O
such	O
as	O
those	O
present	O
in	O
antivirus	B-Application
software	I-Application
,	O
cannot	O
detect	O
this	O
virus	O
having	O
infected	O
a	O
system	O
.	O
</s>
<s>
A	O
way	O
to	O
remove	O
AIDS	B-Application
II	I-Application
manually	O
is	O
to	O
check	O
for	O
EXE	O
files	O
with	O
an	O
identically	O
named	O
COM	O
file	O
8,064	O
bytes	B-Application
in	O
length	O
.	O
</s>
<s>
According	O
to	O
Symantec	O
,	O
AIDS	B-Application
II	I-Application
may	O
play	O
a	O
melody	O
and	O
display	O
the	O
following	O
string	O
:	O
</s>
