1. Disable the self-defense module. To disable the avast! Self-defense module:
Right click avast! tray icon --> program settings -->'Troubleshooting' tab --> check- 'Disable avast! self-defense module'2. Locate and rename the file "asw5Not2.exe". It should be located in the Avast4 folder.
3. Re-enable the self-defense module.
This was apparently part of a virus definition update, even though it has nothing to do with virus definitions.