Twitter account hacked?!

Yesterday I found a notification off @ThunderThumbs (Peter Clark) saying he'd received a Direct Message from me that looked like spam. I don't send spam DMs and if I did I'd be in trouble, reported to twitter, but it was suspected that someone had hacked into my account without my permission! Question is how did they get my password and other details? It wasn't yet known, but after seeing the notification I was worried sick!