I suppose you have to have four avast! services running.
C:\Program Files\Alwil Software\Avast4\ashServ.exe (avast! antivirus service)
C:\Program Files\Alwil Software\Avast4\ashUpdSv.exe (avast! Update Service)
C:\Program Files\Alwil Software\Avast4\ashWebSv.exe (avast! Web Scanner service)
C:\Program Files\Alwil Software\Avast4\ashMaiSv.exe (avast! e-Mail Scanner service)
C:\Program Files\Alwil Software\Avast4\ashdisp.exe (is the 'icon' on the system tray).
You can configure the providers you want, the sensitivity you need or want...
To be full protected you should use the default seetings but you can customize almost everything here