Same happened to me about April this year. Can't remember the wording of the pop up window, it seemed to be from msn/hotmail but it was to the effect, is this other email addy attributed to your Orange mail account?
I was given a four digit code to enter after logging in to my hotmail/msn account. After thinking a little Umm
I changed my hotmail password. I've noticed no anomalies, nor from friends receiving 'funny' mails from me Originally, I thought it might facebook doing some 'mine sweeping'
Daz