In computer science, an "ActiveX control", sometimes called an ActiveX component, is a reusable software component based on Microsoft's Component Object Model (COM). Such components provide encapsulated reusable functionality to programs and they are typically but not always visual in nature.

A Brief Description

ActiveX is a software module that emerged from Microsoft's Component Object Model (COM) and Object Linking and Embedding (OLE) technologies. In 1996, Microsoft took OLE 2.0 and renamed it ActiveX. While the primary role of OLE is to manage documents that utilize multi-media, it also is capable of transferring data between applications. Embedding information is common practice for web designers and these components are frequently found on Internet sites particularly those rich in multi-media content. Web pages utilizing ActiveX function in a similar fashion to server-based applications and behave like standard executable programs. Conceptually, they are like Java applets and share similar implementation characteristics.

ActiveX components can easily blend in and can offer a variety of functionality to programs. They can be used by several applications on a computer or shared on a network. While these components can be utilized for common operating tasks by Macintosh and Microsoft systems, they are most often downloaded and used by web pages for animation displays, for programmatic tasks, or to augment UI functions so as to include items such as spreadsheets, toolbars and similar components.

With today's standards and common practices, most web browser configurations notify and prompt the user prior to the download of an ActiveX control. This can be a difficult choice if there is no guarantee or indication as to the function of the component and the requirement of the web page. Once the user accepts and the component is downloaded, considerable latitude is achieved - the ActiveX control now has the same privileges as the user. This poses security risks that including reading from, and writing to, the registry; manipulation of the user's local file system; and alteration of security rights.

While there are legitimate uses that provide visual display of web content or can functionally enhance the system, there are ActiveX components designed in such a way as to bring about significant malicious and damaging effects. ActiveX technology has been a handy and efficient vehicle for spyware/adware distribution, as well as activation and even propagation of malware. Programmers can embed spyware, Trojan horses, and virus infections to create rogue ActiveX technology.

Safety and security

The security concerns associated with ActiveX control is mainly due to the fact that ActiveX controls can do almost anything that a normal application can. Therefore, both malware and useful form ActiveX controls exists;thereforethe threat level of an ActiveX control can be associated with how trusted its author is.

However, there is one famous case of ActiveX controls safety concern: Internet Explorer. Internet Explorer has the ability to run ActiveX controls within a web page. This is both a blessing and a pain.

ActiveX controls Adobe Reader, Adobe Flash Player, Apple QuickTime Player, Microsoft Windows Media Player, Real Networks RealPlayer, and Sun Java Virtual Machine are routinely used by Internet surfers every hour of a day all across the globe.

However, opening a web page that contains a harmful ActiveX control, and then allowing Internet Explorer to run that harmful control, would be same as running a malware on the computer. Fortunately, Internet Explorer 6 and Windows Vista have taken actions to reduce such risks.

Browser support

Internet Explorer on Windows

Mozilla and Firefox on Windows, with plugin

Writing ActiveX controls

ActiveX Control being created in Visual Basic 6.0

ActiveX controls are simply COM objects, so they can be written using:

Microsoft Foundation Classes (MFC) – Generally not recommended, due to the size of the MFC DLLs required

Active Template Library (ATL) – The frequently accepted simplest way

Languages that support COM, like plain C/C++ or even assembler – Considered to be the most difficult since lots of support code must be written

Languages that provide special support for writing controls e.g. Visual Basic