<s>
MDEF	B-Operating_System
was	O
a	O
computer	O
virus	O
affecting	O
Macintosh	B-Device
machines	O
.	O
</s>
<s>
The	O
first	O
,	O
MDEF	B-Operating_System
A	O
(	O
aka	O
Garfield	O
)	O
,	O
was	O
discovered	O
in	O
May	O
1990	O
.	O
</s>
<s>
MDEF	B-Operating_System
A	O
,	O
B	O
,	O
and	O
C	O
can	O
infect	O
application	O
files	O
and	O
system	O
files	O
,	O
and	O
sometimes	O
document	O
files	O
as	O
well	O
.	O
</s>
<s>
MDEF	B-Operating_System
D	O
can	O
sometimes	O
damage	O
applications	O
beyond	O
repair	O
.	O
</s>
