It happened to me right after merging my account with my battle.net one. I was not at home at the time and didn't have access to internet. The hacker had 2 days to do what he wanted with my character.
The hacker used my main character to farm gold(Aka do all my dailies, mine 30 stacks of saronite ore and 7 of titanium then sell them all on the Auction House and make a shitload of money). He sent the gold to his main character and deleted all my alts.
When I finally got home and realized I was hacked I contacted Blizzard ASAP, got my account and my alts back and also got every single gold the hacker made using my character and every single piece of ore he farmed.
Getting hacked was the best thing that ever happend to my account.