It is supposed to help fight against phishing. The login box asks you to enter your Verified by Visa password, and also shows your "personalized message" (you set this when you register for Verified by Visa).
Recently, my forums got phished big time. A replica login page with a similar looking URL caused 100s of people to get hacked.
Now, it got me thinking:
1. User clicks "login" on IPB
2. Types in the "user name"
3. Ajax grabs their "personalized message" (which they set during registration)
4. The "personalized message" is shown in a third field called "personalized message"
5. Then, once it is shown, the password field is unlocked (disabled=false)
6. The user is happy to enter their password in a place that knows their "personalized message"

If I don't see my personalized message, then I know something is wrong!
Also, use GD library (not plain text) to show the personalized message and randomize the name of the image, etc. That way, nobody can just open a hidden iframe with your login page, and remotely grab the personalized message. (they can with PHP, ... but you can block requests from their server... or use some other methods to stop somebody file_get_contents'ing or cURL-ing it)
