<s>
In	O
computing	O
terminology	O
,	O
a	O
macro	B-Application
virus	I-Application
is	O
a	O
virus	O
that	O
is	O
written	O
in	O
a	O
macro	O
language	O
:	O
a	O
programming	O
language	O
which	O
is	O
embedded	O
inside	O
a	O
software	O
application	O
(	O
e.g.	O
,	O
word	O
processors	O
and	O
spreadsheet	O
applications	O
)	O
.	O
</s>
<s>
Some	O
applications	O
,	O
such	O
as	O
Microsoft	B-Application
Office	I-Application
,	O
Excel	B-Application
,	O
PowerPoint	B-Application
allow	O
macro	O
programs	O
to	O
be	O
embedded	O
in	O
documents	O
such	O
that	O
the	O
macros	O
are	O
run	O
automatically	O
when	O
the	O
document	O
is	O
opened	O
,	O
and	O
this	O
provides	O
a	O
distinct	O
mechanism	O
by	O
which	O
malicious	O
computer	O
instructions	O
can	O
spread	O
.	O
</s>
<s>
Many	O
antivirus	B-Application
programs	I-Application
can	O
detect	O
macro	B-Application
viruses	I-Application
;	O
however	O
,	O
the	O
macro	B-Application
virus	I-Application
 '	O
behavior	O
can	O
still	O
be	O
difficult	O
to	O
detect	O
.	O
</s>
<s>
A	O
macro	O
is	O
a	O
series	O
of	O
commands	O
and	O
actions	O
that	O
helps	O
automating	O
some	O
tasks	O
-	O
usually	O
a	O
quite	O
short	O
and	O
simple	O
program	B-Application
.	O
</s>
<s>
A	O
macro	B-Application
virus	I-Application
can	O
be	O
spread	O
through	O
e-mail	O
attachments	O
,	O
removable	B-Device
media	I-Device
,	O
networks	B-Architecture
and	O
the	O
Internet	O
,	O
and	O
is	O
notoriously	O
difficult	O
to	O
detect	O
.	O
</s>
<s>
A	O
common	O
way	O
for	O
a	O
macro	B-Application
virus	I-Application
to	O
infect	O
a	O
computer	O
is	O
by	O
replacing	O
normal	O
macros	O
with	O
a	O
virus	O
.	O
</s>
<s>
The	O
macro	B-Application
virus	I-Application
replaces	O
regular	O
commands	O
with	O
the	O
same	O
name	O
and	O
runs	O
when	O
the	O
command	O
is	O
selected	O
.	O
</s>
<s>
Once	O
a	O
file	O
containing	O
a	O
macro	B-Application
virus	I-Application
is	O
opened	O
,	O
the	O
virus	O
can	O
infect	O
the	O
system	O
.	O
</s>
<s>
Macro	B-Application
viruses	I-Application
have	O
been	O
used	O
as	O
a	O
method	O
of	O
installing	O
software	O
on	O
a	O
system	O
without	O
the	O
user	O
's	O
consent	O
,	O
as	O
they	O
can	O
be	O
used	O
to	O
download	O
and	O
install	O
software	O
from	O
the	O
internet	O
through	O
the	O
use	O
of	O
automated	O
key-presses	O
.	O
</s>
<s>
Since	O
a	O
macro	B-Application
virus	I-Application
depends	O
on	O
the	O
application	O
rather	O
than	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
it	O
can	O
infect	O
a	O
computer	O
running	O
any	O
operating	B-General_Concept
system	I-General_Concept
to	O
which	O
the	O
targeted	O
application	O
has	O
been	O
ported	O
.	O
</s>
<s>
In	O
particular	O
,	O
since	O
Microsoft	O
Word	O
is	O
available	O
on	O
Macintosh	B-Device
computers	O
,	O
word	O
macro	B-Application
viruses	I-Application
can	O
attack	O
some	O
Macs	O
in	O
addition	O
to	O
Windows	O
platforms	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
macro	B-Application
virus	I-Application
is	O
the	O
Melissa	O
virus	O
which	O
appeared	O
in	O
March	O
1999	O
.	O
</s>
<s>
Not	O
all	O
macro	B-Application
viruses	I-Application
are	O
detected	O
by	O
antivirus	B-Application
software	I-Application
.	O
</s>
<s>
Due	O
to	O
the	O
prevalence	O
of	O
macro	B-Application
viruses	I-Application
,	O
starting	O
with	O
Microsoft	B-Application
Office	I-Application
2007	I-Application
,	O
Microsoft	O
assigned	O
a	O
separate	O
set	O
of	O
file	O
extensions	O
ending	O
in	O
"	O
m	O
"	O
to	O
Office	O
files	O
containing	O
macros	O
in	O
order	O
to	O
prevent	O
users	O
from	O
opening	O
macro	O
virus-infected	O
files	O
that	O
were	O
not	O
intended	O
to	O
contain	O
macros	O
in	O
the	O
first	O
place	O
.	O
</s>
