Managing personal Outlook.com account settings, security, and privacy
Argel, this is not the issue people seem to be having. It is the issue of Microsoft automatically listing any newly used device as a "Trusted Device". Changing these settings as you have suggested does not prevent other browsers such as Firefox or Chrome from accessing outlook.com automatically without login. The need to go to Microsoft.com and proceed to the additional Security settings to disable all trusted devices. After that they will be able to sign-in manually. The "keep me signed in" checkbox has absolutely nothing to do with a lot of these peoples' issues on this forum.