HTML Application (HTA) Filename extension
Developed by Microsoft Website http://msdn.microsoft.com/en-us/library/ms536471(VS.85).aspx
An HTML Application (HTA) is a Microsoft Windows program whose source code consists of HTML, Dynamic HTML, and one or more scripting languages supported by Internet Explorer, such as VBScript or JScript. The HTML is used to generate the user interface, and the scripting language is used for the program logic. An HTA executes without the constraints of the internet browser security model; in fact, it executes as a "fully trusted" application.
The usual file extension of an HTA is
The ability to execute HTAs was introduced to Microsoft Windows in 1999, along with the release of Microsoft Internet Explorer 5. 
HTAs give the developer the features of HTML together with the advantages of scripting languages. They are popular with Microsoft system administrators who use them for system administration tasks, such as user-forms and pre-written network queries, since, for example, VBScript and JScript can access the Windows Task Manager. In general, HTA's are said to be suitable for many purposes, from prototypes to "full-scale" applications, especially where flexibility and speed of development are critical.
An HTA is executed using the program
mshta.exe, or, alternatively, double-clicking on the file. This program is typically installed when Internet Explorer is installed.
mshta.exeexecutes the HTA by instantiating the Internet Explorer rendering engine (mshtml) as well as any required language engines (such as vbscript.dll).
An HTA is treated like any executable file with extension
.exe. When executed via mshta.exe (or the file icon is double-clicked), it runs immediately. When executed via the browser, the user is asked once, before the HTA is downloaded, whether or not to save or run the application; if saved, it can simply be run on demand after that.
When a regular HTML file is executed, the execution is confined to the security model of the web browser, that is, it is confined to communicating with the server, manipulating the page's object model (usually to validate forms and/or create interesting visual effects) and reading or writing cookies.
On the other hand, an HTA runs as a fully trusted application and therefore has more privileges than a normal HTML file; for example, an HTA can create, edit and remove files and registry entries. Although HTAs run in this 'trusted' environment, querying Active Directory can be subject to Internet Explorer Zone logic and associated error messages.
To customize the appearance of an HTA, a new (optional) tag
hta:applicationwas introduced to the
HEADsection. This tag exposes a set of attributes that enable control of border style, the program icon, etc., and provide information such as the argument (commandline) used to launch the HTA. 
Otherwise, an HTA has the same format as an HTML page.
An existing HTML file (with file extension
.html, for example) can be changed to an HTA by simply changing the extension to
This is an example of Hello World as an HTML Application.
<HTML> <HEAD> <HTA:APPLICATION ID="HelloExample" BORDER="thick" BORDERSTYLE="complex"/> <TITLE>HTA - Hello World</TITLE> </HEAD> <BODY> <H2>HTA - Hello World</H2> </BODY> </HTML>
- Active Scripting
- XUL and XULRunner - a language and environment for Mozilla cross-platform applications that resemble the mechanism of HTML Applications
- ^ Article ID:200874 in Microsoft Support, in Microsoft Support Knowledge Base
- ^ Introduction to HTML Applications (HTAs), in MSDN Library
- ^ Why Use HTAs, in MSDN Library, Introduction to HTML Applications
- ^ HTA:APPLICATION Object, in MSDN Library, the complete specification of the tag
- ^ HTA Helpomatic
- ^ HTAEdit, an editor for HTAs with a built-in debugger
- HTML Component (HTC) Reference at MSDN. An HTC encapsulates specific functionality or behavior within HTAs.
- The Script Center, The Script Center, home of Hey, Scripting Guy! Blog
- Learn About Scripting for HTML Applications (HTAs), a tutorial site for learning about HTA's
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