Hi,
is avast uptodate ?
can you do a manual update ?

Please read

http://www.avast.com/i_idt_1378.html

for info & removal (manual or with Tool AvastCleaner)

P.S.: That someone got an infected email with your sender-address doesn’t mean that you are infected:
sobig fakes sender adresses

:wink: :slight_smile: