With the newest version of Avast! that just updated today, the problem is back.
There is a REALLY EASY way to get around this, as the problem file is found within the Application Data cache files (NOT THE ONES IN THE PROGRAM DATA OR THE PROGRAM FILES directories).
In Windows XP, go here:
C:\Documents and Settings\All Users\
You'll see one or more Blizzard Entertainment folders. TRASH ALL OF THEM. Don't worry. When you get logged into the game, the whole folder will be replaced...it's a temporary file.
In Windows Vista, in the Start Menu, use the RUN command, and type this:
C:\Users\TypeYourVistaUserNameHere\AppData\
This will take you to that directory, where you'll see these three folders, in the directory at the left:
Local
LocalLow
Roaming
In that directory, click on "Local" and you'll see (in the righthand pane) all the applications with temporary settings. Find ANY/ALL Blizzard Entertainment folders, and delete them. Don't worry...as with the XP setup, these are temporary files, that the game will replace immediately.
That's it. LOG INTO WoW (or whatever other Blizzard.net game you are wanting to play).
You won't have to do this again until the next Avast! update. If Avast! and Blizzard have solved the FALSE POSITIVE problem, all will be well. If they have NOT solved the problem, you will have to do this step over again. I'm sure the two companies WILL solve the problem soon, permanently. So chill, and do the above steps, and play your game. Hope to see you there! (grin)
I should note that when you get logged in, your computer will sound like it's going CRAZY for a few minutes. Don't worry...this is because it's rebuilding the Blizzard Entertainment file that you deleted, with a nice, fresh copy. In a few minutes, your computer will get back to normal.