The new Windows Live Hotmail includes several new security features, notable among which, is the Single-use Code feature, which you can use for a Hotmail Sign in.
A single-use code is a code you can use instead of your password when you sign in with your Windows Live Hotmail ID.
When you request a single-use code, Hotmail will send it in a text message to a mobile phone number that you’ve added to your Windows Live account.
Each code acts as a one-time substitute for your password and can be used only one time, but you can request one whenever you need one.
If you’re signing in on a public computer—like at the library or school—using a single-use code helps keep your account information secure, since you won’t have to type your password into a public computer, thereby helping to prevent it from being stolen by key loggers and other malware.