A Microsoft file hosting and synchronization service.
Hello,
Microsoft cannot prevent others from "ATTEMPTING" to sign into your account. If they know your username/email address, anyone can attempt to sign in.
What Microsoft can do is providing you with the necessary tools so that you can use them to protect your account.
Please go to your account https://account.live.com > Security, and review the log in activities, are these failed attempts, or actual successful log in?
You can always change your password, and make sure you have two-factor turned on, and it is always better to use authenticator app as well.
In addition, if you want to take one step further - Go to your Microsoft account online https://account.live.com> Sign in > Your info > Sign in preference. Add an alias - You have two options here:
Create new: this will allow you to use the native domain outlook.com to create a new alias.
Add existing: this will allow you to add a 3rd party email address, such as yahoo, gmail, as long as they are not already associated with another Microsoft account.
Once added, make this new alias your primary alias, do NOT delete the old alias. Then at the bottom, click on "Change sign in preference". On the next page, uncheck the box for the old alias. This means, from now one, the old alias cannot be used to sign into your Microsoft account, but it can be still used to receive emails, etc.