With Avast version 9.0.2006 the computer could access the internet but none of the other computers on the network could ping or do file sharing with that computer. Repair and reboot didn’t help. I updated to Avast 9.0.2007 and so far all problems are resolved. Go to Settings > Update > Program > Update. I think they put this update option in a confusing area and it wasn’t asking me if I wanted to update even though I’d set it to ask when new versions were available.