I was gonna start a new thread but there seems to be a lot of you with HTTPS issues already, just gonna add my 2 cents here.
(I'm only having issues with a 4th computer (Win7), the other three work fine (2xWin7+1Win8.1).)
The HTTPS scan seem to block all browsers (IE,FF & Chrome) from https, saying that i.e. google.com is unsafe due to sec_error_expired_certificate (valid from 5th november). And no, my date+time is not set incorrectly. It even states the correct PC date next to the text that says it's expired in firefox...
However while disabling the scan made surfing normal again, avast seem to have removed some addons from chrome (Adblock Plus for example).
Hope avast fixes this soon.