While I was AWAY for 2 days and the computer was OFF, my email account has apparently  sent 'Private Message' to everyone I've ever emailed! What can I do?

Hotmail is meant to be secure: what's going on?

I checked the time and date of one of the 'Private Messages' and it was around 9am on 12th July, in fact I was at home 2 miles away feeling ill.

The only other thing I know is that on Monday 9th July one of my best friends allegedly sent me a 'Private Message'. I couldn't open it, it was an ad for
an i-phone or something like that, which I can't afford and don't want. It asked questions I didn't understand and then it crashed. At the time I wondered
why my friend sent it, then I forgot about it. Now I know she probably didn't send it at all!