And this is the reason why you never ever give anyone your account information...
Maybe you are fine and their intention is pure but their comp has a keylogger...maybe you got a keylogger, if he doesnt...maybe he shared it forward....maybe he stole from you...as long as you dont give your account info to anyone, the chance of getting hacked like that drops to like "notevenworthtomentioning", since who will really want to hack an account in a woltk private server.
I am not saying its impossible but it is highly unlikely...You learned the lesson the hard way. I am playing here since 2011 and I never got hacked...simply because I dont want to give my information to anyone and I also dont want any information about anyone's else's accounts ever.
People asked me to play their chars, never wanted...(if something goes wrong, they would suspect you amongst everyone else and that is simple to avoid by just not doing it)
Besides, changing everything out you should also check your computer for malware, in fact, you should do that first.