As reported on Microsoft community, this has become a real problem from many users, who are receiving streams of "suspicious activity" emails from Microsoft, which are generated by "suspicious activity" from Microsoft own IP addresses (IP 13.101.121.*** and 13.101.120.***). No amount of password changing resolves the issue. But Microsoft is being extremely reticent at explaining the problem to users. Microsoft needs to "come clean" with users, explain what is causing this issue and then resolve it quickly.