Reasons why you received an unusual sign in activity email Even if they know the correct password to your account, they won't be able to take full control over it. This provides a second layer of protection. Microsoft automatically sends you an email about the login attempt, as well as an SMS alert. When Microsoft detects a suspicious log-in attempt, it gets flagged.
People with bad intentions might try to log into your account and use it without your permission. Like other huge corporations, Microsoft looks out for you as a user and your account.