<s>
nVIR	B-Operating_System
is	O
an	O
obsolete	O
computer	O
virus	O
which	O
can	O
replicate	O
on	O
Macintosh	B-Device
computers	I-Device
running	O
any	O
System	O
version	O
from	O
4.1	O
to	O
OS	O
8	O
.	O
</s>
<s>
The	O
source	O
code	O
to	O
the	O
original	O
nVIR	B-Operating_System
has	O
been	O
made	O
widely	O
available	O
,	O
and	O
so	O
numerous	O
variants	O
have	O
arisen	O
.	O
</s>
<s>
nVIR	B-Operating_System
spreads	O
through	O
any	O
nVIR-infected	O
program	O
,	O
but	O
due	O
to	O
the	O
long	O
period	O
of	O
time	O
nVIR	B-Operating_System
lies	O
basically	O
dormant	O
in	O
a	O
host	O
system	O
,	O
nVIR	B-Operating_System
generally	O
finds	O
its	O
way	O
into	O
system	O
backups	O
and	O
is	O
not	O
detected	O
until	O
the	O
first	O
overt	O
symptoms	O
appear	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
disk	O
used	O
in	O
an	O
infected	O
Macintosh	B-Device
is	O
removed	O
and	O
inserted	O
in	O
a	O
second	O
Macintosh	B-Device
,	O
the	O
other	O
machine	O
will	O
become	O
infected	O
if	O
any	O
application	O
on	O
that	O
disk	O
is	O
executed	O
in	O
the	O
second	O
machine	O
.	O
</s>
<s>
Further	O
,	O
any	O
method	O
used	O
to	O
transfer	O
programs	O
between	O
Macintoshes	B-Device
will	O
spread	O
nVIR	B-Operating_System
,	O
including	O
file	O
transfer	O
over	O
a	O
network	O
.	O
</s>
<s>
However	O
,	O
nVIR	B-Operating_System
cannot	O
spread	O
via	O
a	O
print	O
network	O
's	O
hardware	O
.	O
</s>
<s>
nVIR	B-Operating_System
carries	O
an	O
additional	O
code	O
resource	O
,	O
CODE	O
256	O
(	O
though	O
some	O
variants	O
carry	O
CODE	O
255	O
)	O
,	O
and	O
patches	O
the	O
jump	O
table	O
to	O
point	O
to	O
it	O
.	O
</s>
<s>
The	O
original	O
application	O
's	O
entry	O
point	O
is	O
saved	O
in	O
the	O
nVIR	B-Operating_System
2	O
resource	O
.	O
</s>
<s>
nVIR	B-Operating_System
introduces	O
to	O
the	O
System	O
file	O
the	O
INIT	O
32	O
resource	O
which	O
is	O
executed	O
at	O
startup	O
,	O
at	O
which	O
time	O
nVIR	B-Operating_System
patches	O
the	O
TEInit	O
trap	O
.	O
</s>
<s>
The	O
nVIR	B-Operating_System
3	O
(	O
or	O
nVIR	B-Operating_System
5	O
)	O
resource	O
is	O
a	O
copy	O
of	O
INIT	O
32	O
.	O
</s>
<s>
An	O
nVIR	B-Operating_System
10	O
resource	O
in	O
the	O
System	O
file	O
will	O
prevent	O
nVIR	B-Operating_System
infection	O
.	O
</s>
<s>
nVIR	B-Operating_System
0	O
resource	O
holds	O
a	O
counter	O
that	O
is	O
set	O
to	O
1000	O
on	O
the	O
first	O
infection	O
of	O
the	O
system	O
.	O
</s>
<s>
When	O
the	O
counter	O
reaches	O
0	O
,	O
nVIR	B-Operating_System
will	O
beep	O
1	O
out	O
of	O
8	O
reboots	O
and	O
1	O
of	O
4	O
infected	O
application	O
launches	O
.	O
</s>
<s>
If	O
MacinTalk	B-Operating_System
is	O
installed	O
in	O
the	O
machine	O
's	O
System	O
folder	O
,	O
the	O
machine	O
may	O
occasionally	O
say	O
"	O
Do	O
n't	O
Panic	O
"	O
.	O
</s>
<s>
nVIR	B-Operating_System
has	O
been	O
known	O
to	O
'	O
hybridize	O
 '	O
with	O
different	O
variants	O
of	O
nVIR	B-Operating_System
on	O
the	O
same	O
machine	O
.	O
</s>
