<s>
Jerusalem	B-Application
is	O
a	O
logic	O
bomb	O
DOS	B-Device
virus	O
first	O
detected	O
at	O
Hebrew	O
University	O
of	O
Jerusalem	B-Application
,	O
in	O
October	O
1987	O
.	O
</s>
<s>
On	O
infection	O
,	O
the	O
Jerusalem	B-Application
virus	I-Application
becomes	O
memory	O
resident	O
(	O
using	O
2kb	O
of	O
memory	O
)	O
,	O
and	O
then	O
infects	O
every	O
executable	B-Application
file	I-Application
run	O
,	O
except	O
for	O
COMMAND.COM	B-Operating_System
.	O
</s>
<s>
COM	O
files	O
grow	O
by	O
1,813	O
bytes	O
when	O
infected	O
by	O
Jerusalem	B-Application
and	O
are	O
not	O
re-infected	O
.	O
</s>
<s>
Executable	B-Application
files	I-Application
grow	O
by	O
1,808	O
to	O
1,823	O
bytes	O
each	O
time	O
they	O
are	O
infected	O
,	O
and	O
are	O
then	O
re-infected	O
each	O
time	O
the	O
files	O
are	O
loaded	O
until	O
they	O
are	O
too	O
large	O
to	O
load	O
into	O
memory	O
.	O
</s>
<s>
The	O
virus	O
code	O
itself	O
hooks	O
into	O
interrupt	B-Application
processing	O
and	O
other	O
low	O
level	O
DOS	B-Device
services	O
.	O
</s>
<s>
For	O
example	O
,	O
code	O
in	O
the	O
virus	O
suppresses	O
the	O
printing	O
of	O
console	O
messages	O
if	O
,	O
for	O
example	O
,	O
the	O
virus	O
is	O
not	O
able	O
to	O
infect	O
a	O
file	O
on	O
a	O
read-only	O
device	O
such	O
as	O
a	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
One	O
of	O
the	O
clues	O
that	O
a	O
computer	O
is	O
infected	O
is	O
the	O
mis-capitalization	O
of	O
the	O
well-known	O
message	O
"	O
Bad	B-Application
command	I-Application
or	I-Application
file	I-Application
name	I-Application
"	O
as	O
"	O
Bad	B-Application
Command	I-Application
or	I-Application
file	I-Application
name	I-Application
"	O
.	O
</s>
<s>
The	O
Jerusalem	B-Application
virus	I-Application
is	O
unique	O
among	O
other	O
viruses	O
of	O
the	O
time	O
,	O
as	O
it	O
is	O
a	O
logic	O
bomb	O
,	O
set	O
to	O
go	O
off	O
on	O
Friday	B-Device
the	I-Device
13th	I-Device
on	O
all	O
years	O
but	O
1987	O
(	O
making	O
its	O
first	O
activation	O
date	O
13	O
May	O
1988	O
)	O
.	O
</s>
<s>
This	O
particular	O
feature	O
,	O
which	O
was	O
not	O
included	O
in	O
all	O
of	O
Jerusalem	B-Application
's	O
variants	O
,	O
is	O
triggered	O
30	O
minutes	O
after	O
the	O
system	O
is	O
infected	O
,	O
significantly	O
slows	O
down	O
the	O
infected	O
computer	O
,	O
thus	O
allowing	O
for	O
easier	O
detection	O
.	O
</s>
<s>
Jerusalem	B-Application
is	O
also	O
known	O
as	O
"	O
BlackBox	O
"	O
because	O
of	O
a	O
black	O
box	O
it	O
displays	O
during	O
the	O
payload	O
sequence	O
.	O
</s>
<s>
If	O
the	O
system	O
is	O
in	O
text	O
mode	O
,	O
Jerusalem	B-Application
creates	O
a	O
small	O
black	O
rectangle	O
from	O
row	O
5	O
,	O
column	O
5	O
to	O
row	O
16	O
,	O
column	O
16	O
.	O
</s>
<s>
As	O
a	O
result	O
of	O
the	O
virus	O
hooking	O
into	O
the	O
low-level	O
timer	O
interrupt	B-Application
,	O
PC-XT	B-Device
systems	O
slow	O
down	O
to	O
one	O
fifth	O
of	O
their	O
normal	O
speeds	O
30	O
minutes	O
after	O
the	O
virus	O
has	O
installed	O
itself	O
,	O
though	O
the	O
slowdown	O
is	O
less	O
noticeable	O
on	O
faster	O
machines	O
.	O
</s>
<s>
Symptoms	O
also	O
include	O
spontaneous	O
disconnection	O
of	O
workstations	O
from	O
networks	O
and	O
creation	O
of	O
large	O
printer	B-Device
spooling	I-Device
files	O
.	O
</s>
<s>
Disconnections	O
occur	O
since	O
Jerusalem	B-Application
uses	O
the	O
'	O
interrupt	B-Application
21h	I-Application
 '	O
low-level	O
DOS	B-Device
functions	O
that	O
Novell	B-Operating_System
NetWare	I-Operating_System
and	O
other	O
networking	O
implementations	O
required	O
to	O
hook	O
into	O
the	O
file	O
system	O
.	O
</s>
<s>
Jerusalem	B-Application
was	O
initially	O
very	O
common	O
(	O
for	O
a	O
virus	O
of	O
the	O
day	O
)	O
and	O
spawned	O
a	O
large	O
number	O
of	O
variants	O
.	O
</s>
<s>
However	O
,	O
since	O
the	O
advent	O
of	O
Windows	B-Application
,	O
these	O
DOS	B-Application
interrupts	I-Application
are	O
no	O
longer	O
used	O
,	O
so	O
Jerusalem	B-Application
and	O
its	O
variants	O
have	O
become	O
obsolete	O
.	O
</s>
<s>
Friday13th	O
(	O
Note	O
:	O
The	O
name	O
can	O
also	O
refer	O
to	O
two	O
viruses	O
that	O
are	O
unrelated	O
to	O
Jerusalem	B-Application
:	O
Friday-13th-440/Omega	O
and	O
Virus-B	O
)	O
,	O
due	O
to	O
its	O
trigger	O
date	O
of	O
Friday	B-Device
the	I-Device
13th	I-Device
.	O
</s>
<s>
Get	O
Password	O
1	O
(	O
GP1	O
)	O
:	O
Discovered	O
in	O
1991	O
,	O
this	O
Novell	O
NetWare-specific	O
virus	O
attempts	O
to	O
gather	O
passwords	O
from	O
the	O
NetWare	B-Operating_System
DOS	B-Device
shell	O
in	O
memory	O
upon	O
user	O
login	O
,	O
which	O
it	O
then	O
broadcasts	O
to	O
a	O
specific	O
socket	O
number	O
on	O
the	O
network	O
where	O
a	O
companion	O
program	O
can	O
recover	O
them	O
.	O
</s>
<s>
Suriv	O
Viruses	O
:	O
Viruses	O
that	O
are	O
earlier	O
,	O
more	O
primitive	O
versions	O
of	O
Jerusalem	B-Application
.	O
</s>
<s>
The	O
Jerusalem	B-Application
virus	I-Application
is	O
considered	O
to	O
be	O
based	O
on	O
Suriv-3	O
,	O
which	O
is	O
a	O
logic	O
bomb	O
triggered	O
when	O
the	O
date	O
is	O
Friday	B-Device
the	I-Device
13th	I-Device
,	O
switching	O
off	O
the	O
computer	O
on	O
the	O
13th	O
.	O
</s>
<s>
The	O
variant	O
is	O
intended	O
to	O
delete	O
every	O
program	O
as	O
it	O
is	O
run	O
every	O
Sunday	O
,	O
but	O
software	B-Error_Name
bugs	I-Error_Name
prevent	O
this	O
from	O
happening	O
.	O
</s>
<s>
Sunday.1.b	O
:	O
An	O
improvement	O
upon	O
Sunday.b	O
which	O
fixes	O
a	O
bug	B-Error_Name
regarding	O
the	O
Critical	O
Error	O
Handler	O
,	O
which	O
causes	O
problems	O
on	O
write-protected	O
disks	O
.	O
</s>
<s>
PSQR	O
(	O
1720	O
)	O
:	O
PQSR	O
infects	O
.COM	O
and	O
.EXE	O
files	O
,	O
but	O
does	O
not	O
infect	O
overlay	O
files	O
or	O
COMMAND.COM	B-Operating_System
.	O
</s>
<s>
It	O
activates	O
on	O
Friday	B-Device
the	I-Device
13th	I-Device
,	O
and	O
will	O
delete	O
any	O
file	O
run	O
that	O
day	O
.	O
</s>
<s>
Garbage	O
is	O
written	O
to	O
the	O
master	B-Device
boot	I-Device
record	I-Device
and	O
the	O
nine	O
sectors	O
after	O
the	O
MBR	O
.	O
</s>
<s>
It	O
increases	O
the	O
size	O
of	O
infected	O
.COM	O
files	O
by	O
1,813	O
bytes	O
and	O
.EXE	O
files	O
by	O
1,808	O
-1	O
,	O
822	O
bytes	O
,	O
but	O
does	O
not	O
infect	O
COMMAND.COM	B-Operating_System
.	O
</s>
<s>
Westwood	B-Application
(	O
Jerusalem-Westwood	B-Application
)	O
:	O
Westwood	B-Application
causes	O
files	O
to	O
grow	O
by	O
1,829	O
bytes	O
.	O
</s>
<s>
If	O
the	O
virus	O
is	O
memory-resident	O
,	O
Westwood	B-Application
deletes	O
any	O
file	O
run	O
during	O
Friday	B-Device
the	I-Device
13th	I-Device
.	O
</s>
<s>
Jerusalem	B-Application
11-30	O
:	O
This	O
virus	O
infects	O
.COM	O
,	O
.EXE	O
,	O
and	O
overlay	O
files	O
,	O
but	O
not	O
COMMAND.COM	B-Operating_System
.	O
</s>
<s>
However	O
,	O
unlike	O
the	O
original	O
Jerusalem	B-Application
virus	I-Application
,	O
it	O
does	O
not	O
re-infect	O
.EXE	O
files	O
.	O
</s>
<s>
Jerusalem-Apocalypse	O
:	O
Developed	O
in	O
Italy	O
,	O
this	O
virus	O
infects	O
programs	O
as	O
they	O
are	O
executed	O
,	O
and	O
will	O
insert	O
the	O
text	O
"	O
Apocalypse	O
!!	O
"	O
</s>
<s>
Jerusalem-VT1	O
:	O
If	O
the	O
virus	O
is	O
memory-resident	O
,	O
it	O
will	O
delete	O
any	O
file	O
run	O
on	O
Tuesday	O
the	O
1st	O
.	O
</s>
<s>
Jerusalem-T13	O
:	O
The	O
virus	O
causes	O
.COM	O
and	O
.EXE	O
files	O
to	O
grow	O
by	O
1,812	O
bytes	O
.	O
</s>
<s>
Jerusalem-Sat13	O
:	O
If	O
the	O
virus	O
is	O
memory-resident	O
,	O
it	O
will	O
delete	O
any	O
program	O
run	O
on	O
Saturday	O
the	O
13th	O
.	O
</s>
<s>
Jerusalem-Czech	O
:	O
The	O
virus	O
infects	O
.COM	O
and	O
.EXE	O
files	O
,	O
but	O
not	O
COMMAND.COM	B-Operating_System
.	O
</s>
<s>
It	O
will	O
not	O
delete	O
programs	O
run	O
on	O
Friday	B-Device
the	I-Device
13th	I-Device
.	O
</s>
<s>
Jerusalem-Czech	O
has	O
a	O
self-recognition	O
code	O
and	O
a	O
code	O
placement	O
that	O
differ	O
from	O
the	O
original	O
Jerusalem	B-Application
,	O
and	O
is	O
frequently	O
detected	O
as	O
a	O
Sunday	O
variant	O
.	O
</s>
<s>
Jerusalem-Nemesis	O
:	O
This	O
virus	O
inserts	O
the	O
strings	O
"	O
NEMESIS.COM	O
"	O
and	O
"	O
NOKEY	O
"	O
in	O
infected	O
files	O
.	O
</s>
<s>
Jerusalem-Captain	O
Trips	O
:	O
Jerusalem-Captain	O
Trips	O
contains	O
the	O
strings	O
"	O
Captain	O
Trips	O
"	O
and	O
"	O
SPITFIRE	O
"	O
.	O
</s>
<s>
If	O
the	O
year	O
is	O
any	O
year	O
other	O
than	O
1990	O
and	O
the	O
day	O
is	O
a	O
Friday	O
on	O
or	O
after	O
the	O
15th	O
,	O
Jerusalem-Captain	O
Trips	O
creates	O
an	O
empty	O
file	O
with	O
the	O
same	O
name	O
as	O
any	O
program	O
run	O
that	O
day	O
.	O
</s>
<s>
On	O
the	O
16th	O
Jerusalem-Captain	O
Trip	O
re-programs	O
the	O
video	B-Device
controller	I-Device
,	O
and	O
on	O
several	O
other	O
dates	O
it	O
installs	O
a	O
routine	O
in	O
the	O
timer	O
tick	O
that	O
activates	O
when	O
15	O
minutes	O
pass	O
.	O
</s>
<s>
Jerusalem-Captain	O
Trips	O
has	O
several	O
errors	O
.	O
</s>
<s>
Jerusalem-J	O
:	O
The	O
variant	O
causes	O
.COM	O
files	O
to	O
grow	O
by	O
1,237	O
bytes	O
and	O
.EXE	O
files	O
by	O
about	O
1,232	O
bytes	O
.	O
</s>
<s>
The	O
virus	O
has	O
no	O
"	O
Jerusalem	B-Application
effects	O
"	O
,	O
and	O
originates	O
from	O
Hong	O
Kong	O
.	O
</s>
<s>
Jerusalem-Yellow	O
(	O
Growing	O
Block	O
)	O
:	O
Jerusalem-Yellow	O
infects	O
.EXE	O
and	O
.COM	O
files	O
.	O
</s>
<s>
Jerusalem-Yellow	O
creates	O
a	O
large	O
yellow	O
box	O
with	O
a	O
shadow	O
in	O
the	O
middle	O
of	O
the	O
screen	O
and	O
the	O
computer	O
hangs	O
.	O
</s>
<s>
Jerusalem-Jan25	O
:	O
If	O
the	O
virus	O
is	O
memory-resident	O
,	O
it	O
will	O
activate	O
on	O
January	O
25	O
and	O
will	O
delete	O
any	O
program	O
run	O
that	O
day	O
.	O
</s>
<s>
Mendoza	O
(	O
Jerusalem	B-Application
Mendoza	O
)	O
:	O
The	O
virus	O
does	O
nothing	O
if	O
the	O
year	O
is	O
1980	O
or	O
1989	O
,	O
but	O
for	O
all	O
other	O
years	O
a	O
flag	O
is	O
set	O
if	O
the	O
virus	O
is	O
memory	O
resident	O
and	O
if	O
the	O
floppy	B-Device
disk	I-Device
motor	O
count	O
is	O
25	O
.	O
</s>
<s>
The	O
flag	O
will	O
be	O
set	O
if	O
a	O
program	O
is	O
run	O
from	O
a	O
floppy	B-Device
disk	I-Device
.	O
</s>
<s>
Danube	O
:	O
The	O
Danube	O
virus	O
is	O
a	O
unique	O
variant	O
of	O
Jerusalem	B-Application
,	O
as	O
it	O
has	O
evolved	O
beyond	O
Jerusalem	B-Application
and	O
only	O
reflects	O
very	O
few	O
parts	O
of	O
it	O
.	O
</s>
<s>
It	O
reserves	O
5	O
kB	O
of	O
DOS	B-Device
base	O
memory	O
,	O
and	O
reserves	O
5	O
sectors	O
on	O
any	O
disk	O
it	O
infects	O
.	O
</s>
<s>
HK	O
:	O
This	O
variant	O
of	O
Jerusalem	B-Application
originates	O
from	O
Hong	O
Kong	O
,	O
and	O
references	O
one	O
of	O
Hong	O
Kong	O
's	O
technical	O
schools	O
in	O
its	O
code	O
.	O
</s>
<s>
Jerusalem-1767	O
:	O
This	O
virus	O
infects	O
.EXE	O
and	O
.COM	O
files	O
,	O
and	O
will	O
infect	O
COMMAND.COM	B-Operating_System
if	O
it	O
is	O
executes	O
.	O
</s>
<s>
Infected	O
files	O
include	O
the	O
strings	O
"	O
**	O
INFECTED	O
BY	O
FRIDAY	O
13th**	O
"	O
or	O
"	O
COMMAND.COM	B-Operating_System
"	O
.	O
</s>
<s>
Jerusalem-1663	O
:	O
This	O
virus	O
infects	O
.EXE	O
and	O
.COM	O
files	O
,	O
including	O
COMMAND.COM	B-Operating_System
.	O
</s>
<s>
Jerusalem-Haifa	O
:	O
This	O
virus	O
infects	O
.EXE	O
and	O
.COM	O
files	O
,	O
but	O
not	O
COMMAND.COM	B-Operating_System
.	O
</s>
<s>
Its	O
name	O
is	O
due	O
to	O
the	O
Hebrew	O
word	O
for	O
Haifa	B-Algorithm
,	O
an	O
Israeli	O
city	O
,	O
being	O
in	O
the	O
virus	O
code	O
.	O
</s>
<s>
Phenome	O
:	O
This	O
virus	O
is	O
similar	O
to	O
the	O
Apocalypse	O
variant	O
,	O
but	O
will	O
infect	O
COMMAND.COM	B-Operating_System
.	O
</s>
