I have generated most of my wallets through brainwallet.org.But the address that got hacked was the only that I used to create a transaction via brainwallet.I don't remember my passphrase since I was just smashing my keyboard writing random characters for about 10-15 seconds it must have been at least 50(though I think it was more than 100) random nonsense characters.I then just copy the addresses and private keys to a notepad and forget the passphrase forever.I am almost sure it has to do nothing with the passphrase.
Smashing your hand on your keyboard isn't really that random, there are patterns that can be predicted. It is very possible somebody cracked your key, as mentioned in this thread new brainwallet cracking software has recently came out and many people are trying lots of different password lists and keybaord patterns etc. It is possible that the brainwallet.org code was changed and the owner stole the BTC that way (another reason brainwallets are so dumb) but nobody has presented any proof of that. Password cracking techniques are quite advanced, pretty much anything you come up with that you think is random can be predicted. I am always shocked by the kinds of passwords people are able to crack, just because it's long and looks random doesn't mean it is uncrackable at all, I seen someone crack a 120+ character salted hash in a couple of hours..