<s>
An	O
HTML	B-Application
Application	I-Application
(	O
HTA	B-Application
)	O
is	O
a	O
Microsoft	B-Application
Windows	I-Application
program	O
whose	O
source	O
code	O
consists	O
of	O
HTML	B-Language
,	O
Dynamic	B-General_Concept
HTML	I-General_Concept
,	O
and	O
one	O
or	O
more	O
scripting	O
languages	O
supported	O
by	O
Internet	B-Application
Explorer	I-Application
,	O
such	O
as	O
VBScript	B-Application
or	O
JScript	B-Language
.	O
</s>
<s>
The	O
HTML	B-Language
is	O
used	O
to	O
generate	O
the	O
user	O
interface	O
,	O
and	O
the	O
scripting	O
language	O
is	O
used	O
for	O
the	O
program	O
logic	O
.	O
</s>
<s>
An	O
HTA	B-Application
executes	O
without	O
the	O
constraints	O
of	O
the	O
internet	B-Application
browser	I-Application
security	O
model	O
;	O
in	O
fact	O
,	O
it	O
executes	O
as	O
a	O
"	O
fully	O
trusted	O
"	O
application	O
.	O
</s>
<s>
The	O
usual	O
file	O
extension	O
of	O
an	O
HTA	B-Application
is	O
.hta	B-Application
.	O
</s>
<s>
The	O
ability	O
to	O
execute	O
HTAs	B-Application
was	O
introduced	O
to	O
Microsoft	B-Application
Windows	I-Application
in	O
1999	O
,	O
along	O
with	O
the	O
release	O
of	O
Microsoft	B-Protocol
Internet	I-Protocol
Explorer	I-Protocol
5	I-Protocol
.	O
</s>
<s>
HTAs	B-Application
give	O
the	O
developer	O
the	O
features	O
of	O
HTML	B-Language
together	O
with	O
the	O
advantages	O
of	O
scripting	O
languages	O
.	O
</s>
<s>
An	O
HTA	B-Application
is	O
executed	O
using	O
the	O
program	O
mshta.exe	O
,	O
or	O
,	O
alternatively	O
,	O
double-clicking	O
on	O
the	O
file	O
.	O
</s>
<s>
This	O
program	O
is	O
typically	O
installed	O
along	O
with	O
Internet	B-Application
Explorer	I-Application
.	O
</s>
<s>
mshta.exe	O
executes	O
the	O
HTA	B-Application
by	O
instantiating	O
the	O
Internet	B-Application
Explorer	I-Application
rendering	O
engine	O
(	O
mshtml	O
)	O
as	O
well	O
as	O
any	O
required	O
language	O
engines	O
(	O
such	O
as	O
vbscript.dll	O
)	O
.	O
</s>
<s>
An	O
HTA	B-Application
is	O
treated	O
like	O
any	O
executable	O
file	O
with	O
extension	O
.exe	O
.	O
</s>
<s>
When	O
executed	O
remotely	O
via	O
the	O
browser	B-Application
,	O
the	O
user	O
is	O
asked	O
once	O
,	O
before	O
the	O
HTA	B-Application
is	O
downloaded	O
,	O
whether	O
or	O
not	O
to	O
save	O
or	O
run	O
the	O
application	O
;	O
if	O
saved	O
,	O
it	O
can	O
simply	O
be	O
run	O
on	O
demand	O
after	O
that	O
.	O
</s>
<s>
By	O
default	O
,	O
HTAs	B-Application
are	O
rendered	O
as	O
per	O
"	O
standards-mode	O
content	O
in	O
IE7	O
Standards	O
mode	O
and	O
quirks	O
mode	O
content	O
in	O
IE5	B-Protocol
(	O
Quirks	O
)	O
mode	O
"	O
,	O
but	O
this	O
can	O
be	O
altered	O
using	O
X-UA-Compatible	O
headers	O
.	O
</s>
<s>
HTAs	B-Application
are	O
dependent	O
on	O
the	O
Trident	O
(	O
MSHTML	O
)	O
browser	B-Application
engine	O
,	O
used	O
by	O
Internet	B-Application
Explorer	I-Application
,	O
but	O
are	O
not	O
dependent	O
on	O
the	O
Internet	B-Application
Explorer	I-Application
application	O
itself	O
.	O
</s>
<s>
If	O
a	O
user	O
removes	B-Application
Internet	I-Application
Explorer	I-Application
from	O
Windows	O
,	O
via	O
the	O
Control	O
Panel	O
,	O
the	O
MSHTML	O
engine	O
remains	O
and	O
HTAs	B-Application
continue	O
to	O
work	O
.	O
</s>
<s>
HTAs	B-Application
continue	O
to	O
work	O
in	O
Windows	O
11	O
as	O
well	O
.	O
</s>
<s>
HTAs	B-Application
are	O
fully	O
supported	O
running	O
in	O
modes	O
equivalent	O
to	O
Internet	B-Application
Explorer	I-Application
versions	O
5	O
to	O
9	O
.	O
</s>
<s>
Further	O
versions	O
,	O
such	O
as	O
10	O
and	O
11	O
,	O
still	O
support	O
HTAs	B-Application
though	O
with	O
some	O
minor	O
features	O
turned	O
off	O
.	O
</s>
<s>
When	O
a	O
regular	O
HTML	B-Language
file	I-Language
is	O
executed	O
,	O
the	O
execution	O
is	O
confined	O
to	O
the	O
security	O
model	O
of	O
the	O
web	B-Application
browser	I-Application
.	O
</s>
<s>
This	O
means	O
it	O
is	O
confined	O
to	O
communicating	O
with	O
the	O
server	O
,	O
manipulating	O
the	O
page	O
's	O
object	B-Application
model	I-Application
(	O
usually	O
to	O
validate	O
forms	O
and/or	O
create	O
interesting	O
visual	O
effects	O
)	O
and	O
reading	O
or	O
writing	O
cookies	B-Application
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
an	O
HTA	B-Application
runs	O
as	O
a	O
fully	O
trusted	O
application	O
and	O
therefore	O
has	O
more	O
privileges	O
than	O
a	O
normal	O
HTML	B-Language
file	I-Language
;	O
for	O
example	O
,	O
an	O
HTA	B-Application
can	O
create	O
,	O
edit	O
and	O
remove	O
files	O
and	O
registry	B-Protocol
entries	O
.	O
</s>
<s>
Although	O
HTAs	B-Application
run	O
in	O
this	O
'	O
trusted	O
 '	O
environment	O
,	O
querying	O
Active	B-Protocol
Directory	I-Protocol
can	O
be	O
subject	O
to	O
Internet	B-Application
Explorer	I-Application
Zone	O
logic	O
and	O
associated	O
error	O
messages	O
.	O
</s>
<s>
To	O
customize	O
the	O
appearance	O
of	O
an	O
HTA	B-Application
,	O
an	O
optional	O
tag	O
hta:application	O
was	O
introduced	O
to	O
the	O
HEAD	O
section	O
.	O
</s>
<s>
This	O
tag	O
exposes	O
a	O
set	O
of	O
attributes	O
that	O
enable	O
control	O
of	O
border	O
style	O
,	O
the	O
program	O
icon	O
,	O
etc.	O
,	O
and	O
provide	O
information	O
such	O
as	O
the	O
argument	O
(	O
command	O
line	O
)	O
used	O
to	O
launch	O
the	O
HTA	B-Application
.	O
</s>
<s>
Otherwise	O
,	O
an	O
HTA	B-Application
has	O
the	O
same	O
format	O
as	O
an	O
HTML	B-Language
page	O
.	O
</s>
<s>
Any	O
text	O
editor	O
can	O
be	O
used	O
to	O
create	O
an	O
HTA	B-Application
.	O
</s>
<s>
Editors	O
with	O
special	O
features	O
for	O
developing	O
HTML	B-Application
applications	I-Application
may	O
be	O
obtained	O
from	O
Microsoft	O
or	O
from	O
third-party	O
sources	O
.	O
</s>
<s>
An	O
existing	O
HTML	B-Language
file	I-Language
(	O
with	O
file	O
extension	O
.htm	B-Language
or	O
.html	B-Language
,	O
for	O
example	O
)	O
can	O
be	O
changed	O
to	O
an	O
HTA	B-Application
by	O
simply	O
changing	O
the	O
extension	O
to	O
.hta	B-Application
.	O
</s>
<s>
HTA	B-Application
have	O
been	O
used	O
to	O
deliver	O
malware	O
.	O
</s>
<s>
One	O
particular	O
HTA	B-Application
,	O
named	O
4chan.hta	O
(	O
detected	O
by	O
antiviruses	O
as	O
JS/Chafpin.gen	O
)	O
,	O
was	O
widely	O
distributed	O
by	O
the	O
users	O
of	O
the	O
imageboard	O
as	O
a	O
steganographic	O
image	O
in	O
which	O
the	O
user	O
were	O
instructed	O
to	O
download	O
the	O
picture	O
as	O
an	O
HTA	B-Application
file	O
,	O
which	O
when	O
executed	O
,	O
would	O
cause	O
the	O
computer	O
to	O
automatically	O
spam	O
the	O
website	O
(	O
evading	O
4chan	O
's	O
CAPTCHA	O
in	O
the	O
process	O
)	O
with	O
alternate	O
variants	O
of	O
itself	O
;	O
it	O
was	O
reported	O
that	O
such	O
attacks	O
were	O
previously	O
delivered	O
in	O
which	O
the	O
user	O
was	O
prompted	O
to	O
save	O
it	O
as	O
a	O
.js	B-Language
file	O
.	O
</s>
<s>
This	O
is	O
an	O
example	O
of	O
Hello	O
World	O
as	O
an	O
HTML	B-Application
Application	I-Application
.	O
</s>
