FYI, I get the same "Threat Detected" pop-up, but have always concluded that it's because Avast (2015) continually finds a file that it cannot scan (something in the boot record). It's a bug that doesn't do any harm, so I just ignore it.
The other bug in 2015 is that if you use Chrome and have EVER had an extension named "Plugins for Google Chrome", it continually (on boot-up) tells me it's malware and do I want Avast to remove it. If I tell it 'yes', it churns for a full 1.5 minutes, and at the end says it failed to remove the item. When I check my extensions, it's not there. Hasn't been there for well over a month, but I still get the message on boot-up.
Incidentally, I never installed that extension. Don't know what it is or where it came from; it just appeared one day over a month ago.