Try running HijackThis to see if any of your programs have been affected.
http://www.soft32.com/download_19015.html
Do a Scan and if you are unsure of deleting anything, you can post the log file(scan results copied in a text file) on any experts forum site.
Click on Fix checked only if you are sure, as trying to fix the issue may result in deleting the affected file.
It would be useful if you have a backup/ CD of all installed programs.
Also, I would refer the following page for more information:
http://forums.techguy.org/security/317600-hosts-file-hijack-please-help.html
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