It seems that more and more people in the US forums (EDIT: TWICE, actually) and the EU forums are reporting that their accounts have been mysteriously compromised, even with their RealID properly configured. People have logged in after yesterday's downtime and partial rollback only to find their characters stripped naked and with no gold at all. If at first it may have seen as the result of some shady business on the part of the user, now evidence seems to point at some people being able to somehow enter your account after playing a public match with them. Many users have reported to have players like "leiyong", "Matthew De Ruyter" (RealID) and "alexbad19 " added to their "Recently Played with" list just before getting "hacked".
No official Blizzard representative (aka "blues") have commented on the matter, besides the normal "check that you're playing in the correct region" and "change your password" stuff.
Edit: Added another thread in the US forums with more recent information.