<s>
ANTI	O
is	O
a	O
computer	O
virus	O
affecting	O
Apple	B-Device
Macintosh	I-Device
computers	I-Device
running	O
classic	B-Application
Mac	I-Application
OS	I-Application
versions	O
up	O
to	O
System	B-Operating_System
6	I-Operating_System
.	O
</s>
<s>
It	O
was	O
the	O
first	O
Macintosh	B-Device
virus	O
not	O
to	O
create	O
additional	O
resources	B-Operating_System
within	O
infected	O
files	O
;	O
instead	O
,	O
it	O
patches	O
existing	O
CODE	O
resources	B-Operating_System
.	O
</s>
<s>
The	O
most	O
commonly	O
encountered	O
strains	O
of	O
ANTI	O
have	O
only	O
subtle	O
effects	O
,	O
and	O
thus	O
can	O
exist	O
and	O
spread	O
indefinitely	O
without	O
being	O
noticed	O
until	O
an	O
antivirus	B-Application
application	I-Application
is	O
run	O
.	O
</s>
<s>
Due	O
to	O
a	O
bug	O
in	O
the	O
virus	O
,	O
it	O
cannot	O
spread	O
if	O
MultiFinder	O
is	O
running	O
,	O
which	O
prevents	O
it	O
from	O
infecting	O
System	B-Operating_System
7	I-Operating_System
and	O
later	O
versions	O
of	O
Mac	B-Application
OS	I-Application
as	O
well	O
as	O
System	O
5	O
and	O
6	O
running	O
MultiFinder	O
.	O
</s>
<s>
All	O
strains	O
carry	O
a	O
payload	O
related	O
to	O
floppy	B-Device
disk	I-Device
access	O
.	O
</s>
<s>
When	O
an	O
infected	O
application	O
calls	O
the	O
MountVol	O
function	O
,	O
the	O
virus	O
checks	O
that	O
the	O
disk	O
is	O
actually	O
a	O
floppy	B-Device
disk	I-Device
,	O
and	O
if	O
so	O
,	O
reads	O
the	O
first	O
sector	B-Application
(	O
512	B-Application
bytes	I-Application
)	O
of	O
track	O
16	O
.	O
</s>
<s>
Then	O
the	O
virus	O
compares	O
the	O
text	O
at	O
an	O
offset	O
8	O
bytes	O
into	O
that	O
sector	B-Application
against	O
the	O
string	O
$16+	O
"	O
%%S	O
"	O
.	O
</s>
<s>
If	O
the	O
text	O
matches	O
,	O
the	O
virus	O
executes	O
the	O
code	O
at	O
offset	O
0	O
of	O
the	O
sector	B-Application
via	O
a	O
JSR	O
.	O
</s>
<s>
Based	O
on	O
this	O
search	O
for	O
an	O
expected	O
string	O
at	O
a	O
specific	O
location	O
on	O
the	O
disk	O
,	O
Danny	O
Schwendener	O
of	O
ETH	O
Zurich	O
hypothesised	O
that	O
ANTI	O
had	O
been	O
intended	O
to	O
form	O
part	O
of	O
a	O
copy	B-Application
protection	I-Application
scheme	O
,	O
which	O
would	O
detect	O
the	O
reorganisation	O
caused	O
by	O
a	O
standard	O
filesystem	O
copy	O
.	O
</s>
<s>
During	O
infection	O
,	O
ANTI	O
clears	O
all	O
resource	O
attributes	O
associated	O
with	O
CODE	O
1	O
,	O
which	O
may	O
cause	O
the	O
infected	O
application	O
to	O
use	O
more	O
memory	O
,	O
particularly	O
on	O
older	O
Macintoshes	B-Device
with	O
64	O
KiB	O
ROMs	O
.	O
</s>
<s>
Unlike	O
preceding	O
Macintosh	B-Device
viruses	O
,	O
ANTI	O
can	O
not	O
be	O
detected	O
by	O
specific	O
resource	O
names	O
and	O
IDs	O
;	O
a	O
slower	O
string	O
comparison	O
search	O
is	O
required	O
in	O
order	O
to	O
find	O
signatures	O
associated	O
with	O
the	O
virus	O
.	O
</s>
<s>
The	O
University	O
of	O
Hamburg	O
's	O
Virus	O
Test	O
Center	O
recommends	O
detection	O
with	O
an	O
antivirus	B-Application
application	I-Application
such	O
as	O
Disinfectant	B-Application
(	O
version	O
2.3	O
and	O
later	O
)	O
,	O
Interferon	O
,	O
Virus	O
Detective	O
,	O
or	O
Virus	O
Rx	O
,	O
while	O
McAfee	O
recommends	O
Virex	B-Operating_System
.	O
</s>
