Browser hijacking can be very difficult to repair. In the worst cases, where links are encrypted and owerwrite good links, you may reformat your system harddrive and restore the system.
"In some cases, these changes are reversible simply by going into internet options and switching them back. Not always, however. Sometimes it's necessary to edit the windows registry (gasp!) to undo the changes made. Sometimes there is even a combination of registry setting and files clandestinely placed on your hard drive that redo your settings every time you reboot the computer.
No matter how often you change your settings back, they are changed again the next time you restart. There have even been cases where internet options have been removed from the tools menu by registry hacking to prevent you from controlling your own computer!
Even AOL has become a browser hijacker by placing their web site free.aol.com in Internet Explorer's trusted sites security zone, thereby bypassing the most frequently used security settings. This occurs after installing their AOL software, AOL Instant Messenger, Netscape 6.x and ICQ2001b has reportedly done this. AOL then exploits this by downloading ActiveX components to your computer without your consent. The CWS trojan also does this".
http://www.spywareinfo.com/articles/hijacked/
One of the best ways to prevent this type of hijacking is by using intrusion software like Abtrusion Protector that monitors your computers's registers and ask if you want to modify register keys. Abtrusion Protector is free for noncommercial use. There are also free software that is good enough.
Some links:
http://www.acelogix.com/freeware.html
http://www.abtrusion.com/
http://www.free-web-browsers.com/sup...ijackers.shtml