Mystery,
Win32:Naith (also known as Avril, Lirva)
is an Internet worm that copies itself into the Windows system folder under a random name and sets following registry entry to execute itself automatically when Windows starts up.
HKLM\Software\Microsoft\Windows\CurrentVersion\ RunAvril Lavigne - Muse
Win32:Naith spreads by sending itself to email addresses gathered from the DBX, MBX, WAB, HTML, EML, HTM, TBB, SHTML, NCH and IDX files.
Avast should have given you the option to Delete, Restore, or Move to chest.
What did you do when the alarm was received?
The Avast Virus Cleaner (free download)will not remove this worm.
I will be back later with the link to a removal tool. Ok?
techie