ActiveX is the framework for defining reusable software components (known as controls) that perform a particular function or a set of functions in a way that is independent of the programming language used to implement them. A software application can then be composed from one or more of these components in order to provide its functionality. Introduction to ActiveX Controls at microsoft.com, accessed 18-Jan-2008

It was introduced in 1996 by Microsoft Corporation as a development of its Component Object Model (COM) and Object Linking and Embedding (OLE) technologies and it is commonly used in its Windows operating system, although the technology itself is not tied to it.

Many Microsoft Windows applications — including many of those from Microsoft Corporation itself, such as Internet Explorer, Microsoft Office, Microsoft Visual Studio, Windows Media Player, etc. — use ActiveX controls to build their feature-set and also encapsulate their own functionality as ActiveX controls which can then be embedded into other applications. Internet Explorer also allows embedding ActiveX controls onto web pages.

ActiveX controls

ActiveX controls — small program building blocks — can serve to create distributed applications that work over the Internet through web browsers. Examples include customized applications for gathering data, viewing certain kinds of files, and displaying animation.

One can compare ActiveX controls in some sense to Java applets: programmers designed both these mechanisms so that web browsers could download and execute them. However, they also differ:

• Java applets can run on nearly any platform, while ActiveX components officially operate only with Microsoft's Internet Explorer web browser and the Microsoft Windows operating system.
• Programmers can grant to ActiveX controls a much higher level of control over Windows than Java applets ever achieve, making them both more powerful and dangerous. Malware, such as computer viruses and spyware, often spreads as ActiveX controls in webpages.

Programmers can write ActiveX controls in any of the following languages/environments:

• MFC
• ATL
• C++
• C#
• Borland Delphi
• Visual Basic

Common examples of ActiveX controls include command buttons, list boxes, dialog boxes, and the Internet Explorer browser.

History

Faced with the complexity of OLE 2.0 and with poor support for COM in MFC, Microsoft rationalized the specifications to make them simpler, and rebranded the technology as ActiveX in 1996. Even after simplification, users still required controls to implement about six core interfaces. In response to this complexity, Microsoft produced wizards, ATL base classes, macros and C++ language extensions to make it simpler to write controls.