Hotmail account

Hi,
I have a Hotmail account for years and years, and last week, when i was accessing it i got a message saying that i need to introduce a code which would be sent by sms and my mobile number appeared on the screen!
I just ignored it, but i still received a sms from +44 778140659 with a 4 digit code.
I didnt inserted, but now i cannot access the account - demands the code.
I am reluctant to insert the code as it seems to me that the account has been hacked!
anybody has any idea of this situation? is it hacking? :(
help... thanks...
Marira