I have experienced very similar things. I have been railing against Yaboo for some time, and blamed that, but the Avast saga is getting seriously un-funny.
It still could be coincidence, but the mail thing does seem to have some of the same characteristics.
I wanted to accept the update, but it spends ages comparing the merits of the paid versions, then does sweet FA. This is on the serious machine, where, as a rule, I don't test new software. I trusted Avast because of the long period of use prior to this. I accept they need to make money, and wonder how they provide so much for so little, ie nowt, but I do want them to be straight-forward when they offer a freebie.
Given that frostbite is running 5 okay, I'll probably scrap mine and reinstall from a new download.