Kieron hayes HAKING MY ACCOUNT!!!!!!!!!!!

Hello,
someone haked my msn account! i changed my password and they still got into my account. i was just on my friends msn account and they had my addie and it showed that i was on. i went on my account and then this kid called kieron hayes who i know from my school he said haking is fun to me and i said have you been haking my account and he said lol. How can i stop him from going on my account??? please help!!!!!!!!!!!!!