Is this an MSN hacker?

Two days ago I got an IM from a friend's MSN SN with a bunch of photobucket links. He said he hadn't been on and especially hadn't sent me that message. Today I got a text from a friend of mine who asked if I was on MSN yesterday because he got a random message from my MSN SN with a bunch of photobucket links. Is this the work of a hacker and if so, should I just change my pword?