<s>
A	O
self-extracting	B-General_Concept
archive	I-General_Concept
(	O
SFX	O
or	O
SEA	O
)	O
is	O
a	O
computer	O
executable	B-Application
program	I-Application
which	O
contains	O
compressed	B-General_Concept
data	I-General_Concept
in	O
an	O
archive	B-Application
file	I-Application
combined	O
with	O
machine-executable	O
program	O
instructions	O
to	O
extract	O
this	O
information	O
on	O
a	O
compatible	O
operating	B-General_Concept
system	I-General_Concept
and	O
without	O
the	O
necessity	O
for	O
a	O
suitable	O
extractor	O
to	O
be	O
already	O
installed	O
on	O
the	O
target	O
computer	O
.	O
</s>
<s>
Self-extracting	B-General_Concept
files	I-General_Concept
are	O
used	O
to	O
share	O
compressed	B-General_Concept
files	O
with	O
a	O
party	O
that	O
may	O
not	O
necessarily	O
have	O
the	O
software	O
to	O
decompress	O
a	O
regular	O
archive	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
the	O
WinRAR	B-Application
installation	O
program	O
is	O
made	O
using	O
the	O
graphical	O
GUI	O
RAR	O
self-extracting	O
module	O
Default.sfx	O
.	O
</s>
<s>
Self-extracting	B-General_Concept
archives	I-General_Concept
contains	O
an	O
executable	O
file	O
module	O
,	O
a	O
module	O
used	O
to	O
run	O
uncompressed	B-General_Concept
files	O
from	O
compressed	B-General_Concept
files	O
.	O
</s>
<s>
Such	O
a	O
compressed	B-General_Concept
file	O
does	O
not	O
require	O
an	O
external	O
program	O
to	O
decompress	O
the	O
contents	O
of	O
the	O
self-extracting	B-General_Concept
file	I-General_Concept
,	O
and	O
it	O
can	O
run	O
the	O
operation	O
itself	O
.	O
</s>
<s>
However	O
,	O
file	O
archivers	O
like	O
WinRAR	B-Application
can	O
still	O
treat	O
self-extracting	B-General_Concept
files	I-General_Concept
as	O
any	O
other	O
compressed	B-General_Concept
files	O
.	O
</s>
<s>
By	O
using	O
a	O
file	O
archiver	O
,	O
users	O
can	O
view	O
or	O
decompress	O
self-extracting	B-General_Concept
files	I-General_Concept
they	O
received	O
without	O
running	O
executable	O
code	O
(	O
for	O
example	O
,	O
if	O
they	O
are	O
concerned	O
about	O
viruses	O
)	O
.	O
</s>
<s>
A	O
self-extracting	B-General_Concept
archive	I-General_Concept
is	O
extracted	O
and	O
stored	O
on	O
a	O
disk	O
when	O
executed	O
under	O
an	O
operating	B-General_Concept
system	I-General_Concept
that	O
supports	O
it	O
.	O
</s>
<s>
Many	O
embedded	O
self-extractors	B-General_Concept
support	O
a	O
number	O
of	O
command	O
line	O
arguments	O
,	O
such	O
as	O
specifying	O
the	O
target	O
location	O
or	O
selecting	O
only	O
specific	O
files	O
.	O
</s>
<s>
Unlike	O
self-extracting	B-General_Concept
archives	I-General_Concept
,	O
non-self-extracting	O
archives	O
only	O
contain	O
archived	O
files	O
and	O
must	O
be	O
extracted	O
with	O
a	O
program	O
that	O
is	O
compatible	O
with	O
them	O
.	O
</s>
<s>
While	O
self-extracting	B-General_Concept
archives	I-General_Concept
cannot	O
be	O
extracted	O
under	O
another	O
operating	B-General_Concept
system	I-General_Concept
,	O
they	O
can	O
usually	O
still	O
be	O
opened	O
using	O
a	O
suitable	O
extractor	O
as	O
this	O
tool	O
will	O
disregard	O
the	O
executable	O
part	O
of	O
the	O
file	O
and	O
extract	O
only	O
the	O
archive	B-Application
resource	O
.	O
</s>
<s>
The	O
self-extracting	B-General_Concept
executable	I-General_Concept
may	O
need	O
to	O
be	O
renamed	O
to	O
contain	O
a	O
file	O
extension	O
associated	O
with	O
the	O
corresponding	O
packer	O
;	O
archive	B-Application
file	I-Application
formats	O
known	O
to	O
support	O
this	O
include	O
ARJ	B-Application
and	O
ZIP	B-General_Concept
.	O
</s>
<s>
Typically	O
,	O
self-extracting	B-General_Concept
files	I-General_Concept
have	O
an	O
.exe	O
extension	O
,	O
just	O
like	O
any	O
other	O
executable	O
file	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
archive	B-Application
may	O
be	O
called	O
somefiles.zip	O
-	O
it	O
can	O
be	O
opened	O
under	O
any	O
operating	B-General_Concept
system	I-General_Concept
by	O
a	O
suitable	O
archive	B-Application
manager	O
which	O
supports	O
both	O
the	O
file	O
format	O
and	O
compression	B-General_Concept
algorithm	I-General_Concept
used	O
.	O
</s>
<s>
It	O
may	O
also	O
be	O
converted	O
into	O
somefiles.exe	O
,	O
which	O
will	O
self-extract	O
under	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
It	O
will	O
not	O
self-extract	O
under	O
Linux	B-Application
,	O
but	O
can	O
be	O
opened	O
with	O
a	O
suitable	O
archive	B-Application
manager	O
.	O
</s>
<s>
Files	O
that	O
are	O
not	O
recognized	O
as	O
archives	O
by	O
archive	B-Application
managers	O
due	O
to	O
their	O
executable	O
extension	O
can	O
be	O
renamed	O
into	O
.zip	B-General_Concept
.	O
</s>
<s>
This	O
works	O
for	O
ZIP	B-General_Concept
archives	I-General_Concept
due	O
to	O
the	O
way	O
the	O
ZIP	B-General_Concept
header	O
is	O
defined	O
,	O
but	O
not	O
necessarily	O
for	O
other	O
less	O
flexible	O
archive	B-Application
format	O
.	O
</s>
<s>
There	O
are	O
several	O
functionally	O
equivalent	O
but	O
incompatible	O
archive	B-Application
file	I-Application
formats	O
,	O
including	O
ZIP	B-General_Concept
,	O
RAR	O
,	O
7z	O
and	O
many	O
others	O
.	O
</s>
<s>
Additionally	O
,	O
there	O
is	O
a	O
distinction	O
between	O
the	O
file	O
format	O
and	O
the	O
compression	B-General_Concept
algorithm	I-General_Concept
.	O
</s>
<s>
A	O
single	O
file	O
format	O
,	O
such	O
as	O
7z	O
,	O
can	O
support	O
multiple	O
different	O
compression	B-General_Concept
algorithms	I-General_Concept
including	O
LZMA	B-General_Concept
,	O
LZMA2	O
,	O
PPMd	B-Algorithm
and	O
BZip2	B-Application
.	O
</s>
<s>
Depending	O
on	O
the	O
options	O
used	O
to	O
create	O
a	O
self-extracting	B-General_Concept
archive	I-General_Concept
,	O
the	O
executable	O
code	O
placed	O
at	O
the	O
beginning	O
may	O
vary	O
.	O
</s>
<s>
Several	O
programs	O
can	O
create	O
self-extracting	B-General_Concept
archives	I-General_Concept
.	O
</s>
<s>
Among	O
the	O
Windows	B-Application
archivers	O
are	O
WinZip	B-Application
,	O
WinRAR	B-Application
,	O
7-Zip	B-Language
,	O
WinUHA	O
,	O
KGB	B-Language
Archiver	I-Language
,	O
Make	O
SFX	O
,	O
the	O
built-in	O
IExpress	B-Application
wizard	O
and	O
many	O
others	O
,	O
some	O
experimental	O
.	O
</s>
<s>
Macintosh	O
users	O
may	O
choose	O
StuffIt	B-Application
,	O
The	B-Application
Unarchiver	I-Application
,	O
or	O
7zX	O
as	O
their	O
archivers	O
.	O
</s>
<s>
There	O
are	O
also	O
programs	O
that	O
create	O
self-extracting	B-General_Concept
archives	I-General_Concept
on	O
Unix	B-Application
as	O
shell	B-Language
scripts	I-Language
,	O
which	O
utilize	O
programs	O
like	O
tar	O
and	O
gzip	O
(	O
which	O
must	O
be	O
present	O
in	O
the	O
destination	O
system	O
)	O
.	O
</s>
<s>
Others	O
(	O
like	O
7-Zip	B-Language
or	O
RAR	O
)	O
can	O
create	O
self-extracting	B-General_Concept
archives	I-General_Concept
as	O
regular	O
executables	O
in	O
ELF	O
format	O
.	O
</s>
<s>
One	O
of	O
the	O
early	O
examples	O
of	O
self-extracting	B-General_Concept
archives	I-General_Concept
is	O
the	O
Unix	B-Application
shar	B-General_Concept
archive	B-Application
,	O
which	O
combined	O
a	O
number	O
of	O
text	O
files	O
into	O
a	O
shell	B-Language
script	I-Language
that	O
recreated	O
their	O
original	O
content	O
after	O
being	O
executed	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
archive	B-Application
both	O
data	O
and	O
executable	O
files	O
with	O
self-extracting	B-General_Concept
archives	I-General_Concept
.	O
</s>
<s>
They	O
must	O
be	O
distinguished	O
from	O
executable	B-Application
compression	I-Application
,	O
where	O
the	O
executable	O
file	O
only	O
contains	O
a	O
single	O
executable	O
,	O
and	O
running	O
the	O
file	O
does	O
not	O
result	O
in	O
the	O
uncompressed	B-General_Concept
file	O
being	O
stored	O
on	O
disk	O
,	O
but	O
in	O
its	O
code	O
being	O
executed	O
in	O
memory	O
after	O
decompression	O
.	O
</s>
<s>
Another	O
benefit	O
is	O
that	O
it	O
reduces	O
the	O
size	O
of	O
files	O
that	O
are	O
n't	O
already	O
efficiently	O
compressed	B-General_Concept
(	O
most	O
compression	B-General_Concept
algorithms	I-General_Concept
cannot	O
reduce	O
the	O
size	O
of	O
already	O
compressed	B-General_Concept
files	O
.	O
</s>
<s>
Compression	O
usually	O
reduces	O
the	O
size	O
of	O
plain	O
text	O
documents	O
,	O
but	O
rarely	O
affects	O
JPEGs	O
or	O
word	B-General_Concept
processor	I-General_Concept
documents	O
,	O
as	O
many	O
modern	O
word	B-General_Concept
processors	I-General_Concept
already	O
involve	O
a	O
certain	O
level	O
of	O
compression	O
)	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
benefits	O
of	O
compressed	B-Application
archives	I-Application
,	O
self-extracting	B-General_Concept
archives	I-General_Concept
can	O
also	O
be	O
used	O
by	O
users	O
without	O
the	O
necessary	O
programs	O
for	O
extracting	O
their	O
contents	O
,	O
as	O
long	O
as	O
they	O
run	O
a	O
compatible	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
A	O
self-extracting	B-General_Concept
archive	I-General_Concept
may	O
still	O
be	O
more	O
convenient	O
for	O
users	O
who	O
do	O
have	O
archive	B-Application
management	O
software	O
.	O
</s>
<s>
As	O
long	O
as	O
the	O
underlying	O
compression	B-General_Concept
algorithm	I-General_Concept
and	O
format	O
allow	O
it	O
,	O
self-extracting	B-General_Concept
archives	I-General_Concept
can	O
also	O
be	O
encrypted	O
for	O
security	O
.	O
</s>
<s>
If	O
a	O
person	O
can	O
guess	O
part	O
of	O
the	O
contents	O
of	O
the	O
files	O
from	O
their	O
names	O
or	O
context	O
alone	O
,	O
an	O
attacker	O
may	O
be	O
able	O
to	O
break	O
the	O
encryption	O
on	O
the	O
entire	O
archive	B-Application
with	O
only	O
a	O
reasonable	O
amount	O
of	O
computing	O
power	O
and	O
time	O
.	O
</s>
<s>
A	O
disadvantage	O
of	O
self-extracting	B-General_Concept
archives	I-General_Concept
is	O
that	O
running	O
executables	O
of	O
unverified	O
reliability	O
,	O
for	O
example	O
when	O
sent	O
as	O
an	O
email	O
attachment	O
or	O
downloaded	O
from	O
the	O
Internet	O
,	O
may	O
be	O
a	O
security	O
risk	O
.	O
</s>
<s>
An	O
executable	O
file	O
described	O
as	O
a	O
self-extracting	B-General_Concept
archive	I-General_Concept
may	O
actually	O
be	O
a	O
malicious	O
program	O
.	O
</s>
<s>
One	O
protection	O
against	O
this	O
is	O
to	O
open	O
it	O
with	O
an	O
archive	B-Application
manager	O
instead	O
of	O
executing	O
it	O
(	O
losing	O
the	O
advantage	O
of	O
self-extraction	O
)	O
;	O
the	O
archive	B-Application
manager	O
will	O
either	O
report	O
the	O
file	O
as	O
not	O
an	O
archive	B-Application
or	O
will	O
show	O
the	O
underlying	O
metadata	O
of	O
the	O
executable	O
file	O
-	O
a	O
strong	O
indication	O
that	O
the	O
file	O
is	O
not	O
actually	O
a	O
self-extracting	B-General_Concept
archive	I-General_Concept
.	O
</s>
<s>
These	O
systems	O
disallow	O
self-extracting	B-General_Concept
archive	I-General_Concept
files	O
unless	O
they	O
are	O
cumbersomely	O
renamed	O
by	O
the	O
sender	O
to	O
,	O
say	O
,	O
somefiles.exe	O
,	O
and	O
later	O
renamed	O
back	O
again	O
by	O
the	O
recipient	O
.	O
</s>
<s>
This	O
technique	O
is	O
gradually	O
becoming	O
less	O
effective	O
,	O
however	O
,	O
as	O
an	O
increasing	O
number	O
of	O
security	O
suites	O
and	O
antivirus	B-Application
software	I-Application
packages	O
instead	O
scan	O
file	O
headers	O
for	O
the	O
underlying	O
format	O
rather	O
than	O
relying	O
on	O
a	O
correct	O
file	O
extension	O
.	O
</s>
<s>
Self-extracting	B-General_Concept
archives	I-General_Concept
will	O
only	O
run	O
under	O
the	O
operating	B-General_Concept
system	I-General_Concept
family	O
and	O
platform	O
with	O
which	O
they	O
are	O
compatible	O
,	O
making	O
it	O
more	O
difficult	O
to	O
extract	O
their	O
contents	O
under	O
other	O
systems	O
.	O
</s>
<s>
Examples	O
of	O
self-extracting	B-General_Concept
archives	I-General_Concept
,	O
which	O
can	O
be	O
run	O
on	O
multiple	O
targets	O
(	O
such	O
as	O
DOS	B-Device
and	O
CP/M	B-Application
)	O
rather	O
than	O
only	O
the	O
archive	B-Application
contents	O
to	O
be	O
usable	O
under	O
multiple	O
systems	O
,	O
are	O
very	O
rare	O
,	O
because	O
they	O
require	O
the	O
embedded	O
decompressor	O
stub	O
to	O
be	O
a	O
fat	O
binary	O
.	O
</s>
<s>
Also	O
,	O
since	O
the	O
self-extracting	B-General_Concept
archives	I-General_Concept
must	O
include	O
executable	O
code	O
to	O
handle	O
the	O
extraction	O
of	O
the	O
contained	O
archive	B-Application
file	I-Application
,	O
they	O
are	O
slightly	O
larger	O
than	O
the	O
original	O
archive	B-Application
.	O
</s>
