Hi there, I too had the CPU constant 97-100% from AvastSvc.exe after installing the program update this morning. Windows XP Home. In case this is useful I thought I'd chime in as there was something else: I tried running an Avast complete scan several times after rebooting and each time it hung up after a few seconds at "tested files: 10" and "tested folders: 1". Dragonfly_27z, have you tried an Avast virus scan [full version], will it run?
I have been running Malwarebytes Pro [real time] and MS Security Essentials as well for a couple of months, frowned on I know, but there were no noticeable problems prior to todays program update.
Don't know how much further information I could give as I removed Avast: I wanted to run a scan with ESET online scanner and IE kept freezing [I usually use Firefox portable, which was freezing up as well, ESET is only available using IE]. IE ran fine after Avast was removed, Firefox is back to normal as well.
The ESET scan came up clean, as well as a Malwarebytes scan and a SuperAntiSpyware scan. I ran rkill a few times in there as well between reboots and it came up blank.
Before removing Avast, I noticed that it would "calm down" for periods as well [as mentioned by Dragonfly], but the system idle process would then show 100% CPU. It would flip between massive system idle process CPU usage and AvastSvc.exe.
OK, there it is, thanks for any info,