A Browser Helper Object (BHO) is a program written to run with a web browser to extend the functionality of the browser. An example is the Gigablast toolbar which is a useful browser helper object. Some browser helper objects may be malicious programs which may be used to take over a computer system.

The browser helper object is a plugin that is designed for specific browsers such as Microsoft's Internet Explorer or Firefox. Some browser helper objects may be used to load malware such as adware, spyware, or trojans. The browser helper object may spy on the computer user's actividties while they are using their browser and even send passwords typed into web pages to a third party.

Some tools have been created that list and help identify browser helper objects that are installed on a computer. One free tool is called HijackThis and is used to list Browser helper objects (BHOs) installed on a computer. This tool can help users find and remove hostile software that may be hijacking their browser settings.