I think I need to specify Avast as a trusted application in Comodo, but dont know to specify the application.
Into the firewall settings, the following programs should be allowed to connect:
C:\Program Files\Alwil Software\Avast4\ashWebSv.exe (avast! Web Scanner)
C:\Program Files\Alwil Software\Avast4\ashMaiSv.exe (avast! e-Mail Scanner Service)
C:\Program Files\Alwil Software\Avast4\Setup\avast.setup (avast! Update executable). This is a temporary file that just appears when an update (check) is about to launch, and disappears again afterwards.
Don't need rights to connect:
C:\Program Files\Alwil Software\Avast4\aswUpdSv.exe (avast! Update Service)
C:\Program Files\Alwil Software\Avast4\ashServ.exe (avast! antivirus service). Although, ashServ.exe sends ping packets to find out if the Internet connection is alive. You can turn this off by checking the "My computer is permanently connected to the Internet" box in the avast Program Settings > Update (Connections) page.