Browser Helper Objects (BHO)
A Browser Helper Object (BHO) is a DLL module that loads everytime you start your browser. Usually, a BHO is installed on your system by another software program or installed when visiting a website. An example of a BHO installed by software is the Adobe PDF plugin so you can read pdf documents without manually starting Acrobat Reader, when surfing the web. An BHO installed by a website is the google toolbar.
BHO's can do "anything" but most of the time they provide some sort of extra functionality to the user like a toolbar. These BHO's require your permission to be installed on the system. Some BHO's get installed secretly or are shipped with a program as a 'third party application' such as the BHO's supplied with Messenger Plus. This last category, the 'hidden' BHO's are a safety threat. Most of the time they'l annoy you by creating dozens of popups or redirecting your site searches. But they can do virtually anything like reading or writeing on your system, sending data about you and your surfing habits etc.
Most BHO's require user approval before being installed even those semi-hidden BHO's, described as third party programs. Ever wondered where information about those third party programs is 'hidden'? It isn't that hard to find, before installing a, usually 'free', program take a good look at the license agreement. If it's too big, select all text (control-a) copy it (control-c) and paste it (control-v) in a word document. Then search (control-f) for terms like 'third (3rd)' or 'third (3rd) party'. See? The info is there but it's hidden in a lot of judicial terms.
Conclusion: most BHO's don't pose any threat, but some do and once you picked up a BHO you undestandably want to get rid off it. But what if you don't know you've got one? Take a look at this page HijackThis this program also lists BHO's or click here BHOdemon.