Having also been through the mill with this little swerve-ball from Avast, I actually believe it's either a huge mistake inadvertently written into an update because the 'every website has malware' problem definitely occurred immediately after an Avast auto update earlier today.
And it has now completely gone away after the new update I have just received minutes ago.
Or, and this is where we enter the realms of conspiracy theory, it's a marketing campaign!
Didn't anyone notice that all the dark red malware detected windows that popped-up only had one link that took you straight over to the "benefits of upgrading page" on the Avast website ??
I wonder how many panic purchased into the pro version during all of this?
Yes Avast is our friend and they provide possibly the best free access virus checker available, but times are hard.
OK I did admit it was only a theory, but I discovered Avast some years ago after going through the hell imposed on free users by AVG when their server was almost impenetrable and no one could update their virus patterns for weeks on end. Strangely the paid for users had no problems at all and AVG simply did not comment on the problem with any real effect.
I pray this is a glitch and Avast doesn't go down the road of 'persuading' potential paying customers by using scare tactics like this.