Playstation network email? bad i think?

playstation network sent me a email that said something about they think my account has been stolen or something. but i never logged in online for a key logger ot get the stuff. and ive been on it once when i first got my ps3. sooo what does it mean? im not even sure what my pass is. and im pretty sure we didn't have our credit card on it. since we didn't buy anything or such. ill put the email in a detail thingy. please help.