ZFR: I was a happy Avast user since around 2005. Few years ago pop-ups started appearing "OMG! Your boot time is 15 secs. There are 836934 problems causing slow-downs. Buy Avast Pro to solve them". OK, this is slightly annoying. I don't mind ads but I hate those kind of scare-crap tactics. Still I decide to keep Avast...
Then, few months later Skype starts mysteriously opening up on start up. I check Skype's settings; make sure all autostarts are disabled. Check the registry.. nothing. It still happens. Then by chance the culprit is found: Avast's recent update has enabled an option to automatically scan and update all my installed software. I'm really pissed now, because I like updating my software myself, and I don't like Avast enabling this option without asking me first.
The final straw however was when I noticed that Avast started adding (again - without me enabling this option) a "scanned by Avast www.(avast's address).com" to all my outgoing emails. It took me time to find this option to disable it, but it seems Avast keeps enabling it from time to time when it updates.
Now a program that tries to spread itself by attaching to a user's outgoing email without his knowledge is almost textbook definition of malware; something that Avast should be protecting me from. And other bad practices of Avast include:
_ Silently deleting some files it thinks are malware, without any warning, despite having my settings set to "Ask me first". It's then makes it as difficult as possible to get to the Virus Chest to restore those files.
_ Auto-updating (program updates; not virus definitions), despite having options set to "ask me first". It often does ask me, but some updates are still made without my approval.
_ Attempting to install Google Chrome when auto-updating; you have to remember to opt out.
_ Installing, by default without asking me - not even an opt-out, features that I never wanted, like some idiotic browser addons.
So sadly, because I really loved it how it was initially, this means that after spending more than 10 years with it, Avast has to go.
I'm not going to defend Avast in any way, but I'd like to update my experiences - they are slightly different.
I've started using Avast at the same time as you. For a long time I was using Windows XP and there weren't any problems with that version. Recently I needed to upgrade my PC so I had to upgrade my system as well (Windows 7 now) and I needed to upgrade or even change a lot of software I used to use.
I've read a lot about "how bad new version of Avast is" so I did a lot of web research myself, later I installed it on virtual machine to test all options and then installed it again on (so called) "my own test installation of OS". After that I had noted down all options I should turn on or off. Since that time I have not experienced such problems like you described.
I know, maybe it was a lot (too much?) of work (most users will not do that), but.. well, it worked for me.