Recently I visited a friend of mine. Her laptop was having Mozilla Firefox from Mozilla Corp. with hijacked search bar from some malicious site.
Hijacked homepage or search means when you open a new tab or do new search you will be redirected to some malicious site with domain parked or ads.
Why a browser search/homepage get replaced ?
In the most of the cases browser get hacked because of installing toolbars or malicious software from untrusted sources. e.g. smiley toolbars, search toolbars, spell check toolbars, radio toolbars.
Another chance is a virus which only deals with browser hijacking. You might be one victim of it.
How to reset homepage/search page of browser ?
1. Uninstall all the toolbars, untrusted softwares you installed recently.
2. Go to browser options and try resetting homepage.
3. Scan PC with any good updated antivirus. Recommended Avira Free Antivir
4. For Firefox users:
Type about:config in address bar. Hit enter.
Search for some part of malicious web url, change value upon found.
5. Look for unknown processes in task manager. End them upon detection. (Use unlocker tool if process is locked by the virus)
6. Go to Run, type regedit. Search for some part of malicious web url, delete value upon found.
7. Restore system to an older state.
8. Install search engine protectors. A software that protects your search engine being changed from default.
9. Reinstall browser.
10. Install search toolbar from famous sites. i.e. Google, Yahoo and it will do the rest for you.