Were you using the same password on both sites?

it's a *really* good idea to use different passwords on trading sites (mtgox) than "bank" sites (mybitcoin).

Your password hashes were released to the world from MtGox, and if it wasn't a *really* good password, then it was compromised pretty quickly.

There's probably nothing mybitcoin can/will/should do about this... it's not really their fault.