Microsoft is said to be in the works of integrating two-factor authentication into its Outlook.com mail service. LiveSide is reporting this morning that security enhancements are being prepped, along with a new authenticator app for Windows Phone.
Google and Apple both already use two-factor authentication processes when you access their services and is the reason that you sometimes have to answer security questions when logging in from a new device. I won't get into how they both work here, but Microsoft's system appears to use the Authenticator App to generate the authentication codes.
LiveSide is also reporting that the new authentication system will not work with Microsoft Accounts that have been linked together, which means that users must un-link multiple accounts. The Authenticator app is already available for download in the Windows Phone Store, so it looks like two-factor authentication for Outlook.com is on the way soon.