<s>
In	O
distributed	B-Architecture
computing	I-Architecture
,	O
code	B-Operating_System
mobility	I-Operating_System
is	O
the	O
ability	O
for	O
running	O
programs	O
,	O
code	B-Language
or	O
objects	O
to	O
be	O
migrated	B-General_Concept
(	O
or	O
moved	O
)	O
from	O
one	O
machine	O
or	O
application	O
to	O
another	O
.	O
</s>
<s>
This	O
is	O
the	O
process	O
of	O
moving	O
mobile	B-Operating_System
code	I-Operating_System
across	O
the	O
nodes	O
of	O
a	O
network	B-Architecture
as	O
opposed	O
to	O
distributed	B-Architecture
computation	I-Architecture
where	O
the	O
data	O
is	O
moved	O
.	O
</s>
<s>
It	O
is	O
common	O
practice	O
in	O
distributed	B-Architecture
systems	I-Architecture
to	O
require	O
the	O
movement	O
of	O
code	B-Language
or	O
processes	O
between	O
parts	O
of	O
the	O
system	O
,	O
instead	O
of	O
data	O
.	O
</s>
<s>
Examples	O
of	O
code	B-Operating_System
mobility	I-Operating_System
include	O
scripts	O
downloaded	O
over	O
a	O
network	B-Architecture
(	O
for	O
example	O
JavaScript	B-Language
,	O
VBScript	B-Application
)	O
,	O
Java	B-Application
applets	I-Application
,	O
ActiveX	B-Application
controls	I-Application
,	O
Flash	B-Operating_System
animations	I-Operating_System
,	O
Shockwave	O
movies	O
(	O
and	O
Xtras	O
)	O
,	O
and	O
macros	O
embedded	O
within	O
Microsoft	B-Application
Office	I-Application
documents	O
.	O
</s>
<s>
The	O
purpose	O
of	O
code	B-Operating_System
mobility	I-Operating_System
is	O
to	O
support	O
sophisticated	O
operations	O
.	O
</s>
<s>
According	O
to	O
a	O
classification	O
proposed	O
by	O
Fuggetta	O
,	O
Picco	O
and	O
Vigna	O
,	O
code	B-Operating_System
mobility	I-Operating_System
can	O
be	O
either	O
strong	O
or	O
weak	O
:	O
</s>
<s>
strong	O
code	B-Operating_System
mobility	I-Operating_System
involves	O
moving	O
both	O
the	O
code	B-Language
,	O
data	O
and	O
the	O
execution	O
state	O
from	O
one	O
host	O
to	O
another	O
,	O
notably	O
via	O
a	O
process	O
image	O
(	O
this	O
is	O
important	O
in	O
cases	O
where	O
the	O
running	O
application	O
needs	O
to	O
maintain	O
its	O
state	O
as	O
it	O
migrates	O
from	O
host	O
to	O
host	O
)	O
,	O
while	O
weak	O
code	B-Operating_System
mobility	I-Operating_System
involves	O
moving	O
the	O
code	B-Language
and	O
the	O
data	O
only	O
.	O
</s>
<s>
Therefore	O
,	O
it	O
may	O
be	O
necessary	O
to	O
restart	O
the	O
execution	O
of	O
the	O
program	B-Application
at	O
the	O
destination	O
host	O
.	O
</s>
<s>
Several	O
paradigms	O
,	O
or	O
architectural	O
styles	O
,	O
exist	O
within	O
code	B-Operating_System
mobility	I-Operating_System
:	O
</s>
<s>
Remote	B-Operating_System
evaluation	I-Operating_System
—	O
A	O
client	O
sends	O
code	B-Language
to	O
a	O
remote	O
machine	O
for	O
execution	O
.	O
</s>
<s>
Code	B-Protocol
on	I-Protocol
demand	I-Protocol
—	O
A	O
client	O
downloads	O
code	B-Language
from	O
a	O
remote	O
machine	O
to	O
execute	O
locally	O
.	O
</s>
<s>
Mobile	B-Operating_System
agents	I-Operating_System
—	O
Objects	O
or	O
code	B-Language
with	O
the	O
ability	O
to	O
migrate	O
between	O
machines	O
autonomously	O
.	O
</s>
<s>
Mobile	B-Operating_System
code	I-Operating_System
can	O
also	O
download	O
and	O
execute	O
in	O
the	O
client	O
workstation	O
via	O
email	O
.	O
</s>
<s>
Mobile	B-Operating_System
code	I-Operating_System
may	O
download	O
via	O
an	O
email	O
attachment	O
(	O
e.g.	O
,	O
macro	O
in	O
a	O
Word	O
file	O
)	O
or	O
via	O
an	O
HTML	O
email	O
body	O
(	O
e.g.	O
,	O
JavaScript	B-Language
)	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
ILOVEYOU	O
,	O
TRUELOVE	O
,	O
and	O
AnnaK	O
emails	O
viruses/worms	O
all	O
were	O
implemented	O
as	O
mobile	B-Operating_System
code	I-Operating_System
(	O
VBScript	B-Application
in	O
a	O
.vbs	B-Application
email	O
attachment	O
that	O
executed	O
in	O
Windows	O
Scripting	O
Host	O
)	O
.	O
</s>
<s>
In	O
almost	O
all	O
situations	O
,	O
the	O
user	O
is	O
not	O
aware	O
that	O
mobile	B-Operating_System
code	I-Operating_System
is	O
downloading	O
and	O
executing	O
in	O
their	O
workstation	O
.	O
</s>
<s>
Mobile	B-Operating_System
code	I-Operating_System
also	O
refers	O
to	O
code	B-Language
"	O
used	O
for	O
rent	O
"	O
,	O
a	O
way	O
of	O
making	O
software	O
packages	O
more	O
affordable	O
.	O
</s>
