Just out of curiosity I ran Kaspersky’s eScan on a computer that has been running Avast for a long time.
It detected 3 viruses never reported by Avast: W32.Wootboot.gen, and two versions of ??Spybot-??? - where ? means a number. Unfortunately I deleted the log when I formatted the HD later that day, so I’m not sure what the exact name was.