Thanks @JagWaugh
The number is so big, so I don’t think it relates to Microsoft employees 
Thanks @Ivan_Rapekas
Actually, we have one website and one forum. They are single sign on.
So user can’t register directly on forum. They register on website, then our website sever sends request api to register them on forum.
And both website and forum are being hosted on Microsoft Azure.
May be this is the root of my problem.
But the IP address was logged is not IP address of my website’s server.
So I still don’t know how was this IP address logged @@