Hacks@Blizzard.com

It depends, they have a massive load of mails daily sometimes it’s just spam or mails with seemingly cheats but not actually so - just bugs or players legitimately multiboxing.

After an investigation, if the players are guilty they may be earmarked for a future banwave. Very rarely do players get banned immediately. A recent banwave already happened at 1 July for example. Actions Taken Against Exploitation -- July 1 Update