I have found that if an upgrade is done properly, avast! 7 is less problematic than avast! 6. In my opinion, proper means:
1) Remove all avast! versions as well as any other A/V programs from add/remove programs in control panel.
2) Download the latest version of avast! Uninstall Utility (aswclear.exe) and save it on your desktop. http://files.avast.com/files/eng/aswclear.exe
3) Start Windows in Safe Mode (F8 key before Windows splash screen on a reboot)
4) Open (execute) the uninstall utility aswclear.exe
5) Choose which version of avast! to uninstall. This process will be repeated for each avast! version (4, 5, and 6) So let’s assume we had all 3 versions of avast! installed at some point. So we choose version 4.8 and proceed.
6) If you installed avast! in a different folder than the default, browse for it. (Note: Be careful! The content of any folder you choose will be deleted!)
7) Click REMOVE
Restart your computer
9) Start Windows in Safe Mode again
10) Open the avast! uninstall utility a second time
11) Choose version 5 of avast!
12) If you installed avast! in a different folder than the default, browse for it.
13) Click REMOVE
14) Restart your computer
15) Start Windows in Safe Mode again
16) Open the uninstall utility again
17) Choose version 6 of avast!
18) If you installed avast! in a different folder than the default, browse for it.
19) Click REMOVE
20) Restart your computer
21) Now install avast! 7 (I personally prefer doing a custom installation)