Google are constantly working on methods to improve the security of accounts hosted on their service. The newest method is dubbed the Login Challenge for suspicious sign-ins. This new feature is being rolled out to all Google Apps customers, include ourselves as Google Apps for Education users, so we may start seeing this over the course of the summer.
So what is the Login Challenge? Here's the answer in Google's own words:
If we detect that an unauthorized person is attempting to access a user's account, we will present them with a Login Challenge that asks the person to verify their identity. This is designed to prevent unwanted access to the account, even if the person has obtained the username and password.
If you're logging in from a new geographical location you've never used before, or failing to get your password right for several times and/or with a new device, you may get a Login Challenge to ensure that it is really you that's accessing your account and not some hacker who stole your password.
Find out more about the Login Challenge, how it works, and how Google verifies you are who you really think you are at the new Securing your Smoogle account page. And once you've done that, check out 2-step authentication for an outstanding way to secure your account and data.