Last night something happened with my e-mail outlook account which I actively use. I'm not sure if it was an accident or a security breach. Around midnight I got several e-mails from Microsoft security asking me to verify my account and saying also if I didn't asked for the confirmation to cancel it. So I did. Then it sent me some security codes saying if I didn't ask for them to change my password. So I did. When I changed the password, it opened the overview data page. It showed me some other information entered in my account that wasn't mine.

 I got scared that someone hacked my account. I still had access to my inbox because I didn't shut down the original window of my browser. But when I tried to enter to my inbox using another tab in my browser, I couldn't. It would send me on that page with that information that weren't mine. 

 The weirdest thing was that in a taskbar was a notification “Microsoft Confidential” in red letters. Meanwhile Outlook popped out a message saying that outlook was updated and to refresh my browser. I still saw my inbox in one window and data info in other browser window. Next I did is to delete all my e-mails thinking that if I shut down the window with my inbox I wouldn't be able to access again. I was trying to log in again in a different browser, but the new password that I set wasn't working and I was thinking what the heck now. Then I tried to use my old password and it worked. 

Everything is OK now. But the thing that got me thinking is that I had another e-mail account and my phone number in security section in case someone tried to hack my account to protect me and nothing came on my mobile saying that someone is trying to take over my account. 

 Can you tell me what happened? Was that a security breach or technical problem from outlook.com? Did someone somehow taken my mail as a primary address? What can I do to prevent this?