I sent already a bug report and opened a thread on the Battle.net ->
http://us.battle.net/hearthstone/en/forum/topic/20042655279As you can see a lot of users are affected, many of them are disabling/uninstalling Avast because they don't know how to restore the binary file.
I'm currently using Avast on 200~ PCs and had
(fortunately) barely any false positives so far, this particular case should get a lot of attention though because it is affecting thousands of users.