Programming - Internet Explorer Plugins

A Browser Helper Object (BHO) is a DLL module designed as a plugin for Microsoft's Internet Explorer web browser to provide added functionality. BHOs were introduced in October 1997 with the release of version 4 of Internet Explorer. Most BHOs are loaded once by each new instance of Internet Explorer. However, in the case of the Windows File Explorer, a new instance is launched for each window.

Some modules enable the display of different file formats not ordinarily interpretable by the browser. The Adobe Acrobat plugin that allows Internet Explorer users to read PDF files within their browser is a BHO.

Other modules add toolbars to Internet Explorer, such as the Alexa Toolbar that provides a list of web sites related to the one you are currently browsing, or the Google Toolbar that adds a toolbar with a Google search box to the browser user interface.

Example code is provided with this article.