App Store asking for credentials?

After trying to install an application on my iPhone 4, I just saw this popup for the first time:

Security Info Required

To help ensure the security of your Apple ID, you must confirm your password and answer your security questions.

     [Cancel]        [Security Info]

Why is this dialog popping up?

Does it happen randomly? Or is it because I connected to a new Wi-Fi hotspot, and the App Store has never seen this IP address before? Or could it be because someone tried logging in with my account several times and failed?

This appears to be a recent change to how purchasing functions, added for increased security. According to TheNextWeb, via MacRumors:

In the past 24 hours, Apple appears to have started prompting iOS devices owners and those with Apple IDs within iTunes to make their accounts more secure, requiring them to pick three security questions and enter their answers when they download a new app.

The company is also asking users to enter a backup email address, in order to better protect their device but also their account (which is tied to Apple’s Retail website and all of its media services).