I'm a player in Icecrown (Wotlk server) and my account has been hacked. I logged on to my toons to see my gold missing. I have no history of letting anyone use my account, nor have I tried to sell my account. I'm also very careful on clicking suspicious links. I found out as well from my guildmates that someone was trying to sell my toons prior to my logging in.
I immediately turned on my two-factor authentication as soon as I found out I was hacked, as well as changed my password. A few hours later, I received a notification via email that someone has tried to access my account again from a different location.
If you changed password and enabled 2 step authentication, your account should be safe now. You get emails about ingame logins even if password was not entered correctly. Stolen gold can not be restored.