You should obviously change anything else that uses that password and never use it again. Out of curiosity, what was the password? A randomly generated 16char password made up of upper & lower case letters numbers and symbols is around 104bits of entropy which is pretty much impossible to crack, it would definitely cost a hell of a lot more than 6BTC worth of computing power to crack, so I'm curious to see how strong your password really was, if it really is that strong the hacker must have keylogged you when you last entered your password and only just got around to stealing the funds.

Maybe the hacker got a backup of your wallet that wasn't encrypted?