Yesterday when I started the World of Warcraft game client it downloaded a small update and then when I tried to log in threw "Battle.net error #112" at me. Judging by description my game files had become corrupted. I did a quick search through WoW forums, but didn't find anything valuable. So I just went to C:\Program Files (x86)\World of Warcraft\Updates and deleted the update file from that folder. At the startup client redownloaded it again, this time successfully.