But because if I go into some web site with Internet Explorer Antivir detect some files as viruse and Avast no?
Depends on avast! configuration...
Depends on what site you're talking about...
Maybe you can send some links to virus (at) avast.com
But, anyway, please, don't post like infected links here.
I have AntiVir (not resident) and avast!
AntiVir has too many false positives (specially macro viruses), slow and huge updates, few update servers, interface weak (in my opinion).
avast! is far much configurable, smart and fast updates, lots of servers for it, beautiful interfaces for all tastes