Update your AV & do a scan, see if it finds anything (maybe a worm Delf.ATB). Or you can try AVG Free AV...that should find it.
AVG Free Advisor: AVG Anti-Virus Free

Download AVG, update it, scan your computer.
Search the forum & you'll see other people have had this problem...AVG has fixed things for the majority

Always make sure that you're using a good AV program. Keep it updated & scan all files that you download before you open them

If you need more help, try one of the sites below.

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