HijackThis is the original, homepage hijacker detector and remover.
Hijack This is for advanced users. If you are not familiar with running processes on your computer as well as anything ever installed that could tie into your web browser, it will not be much help to you. Finally, Hijack This has been taken over by Trend Micro. This new version can be http://www.majorgeeks.com/Trend_Micro_HijackThis_d5554.htmldownloaded here.
You should have scanned your machine with anti-spyware, virus and trojan tools before using Hijack This.
Initially based on the article Hijacked!, but expanded with almost a dozen other checks against hijacker tricks. It does not target specific programs/URLs, just the methods used by hijackers to force you onto their sites.