Adnan Masood's Weblog! عدنان مسعود

It seemed like an attempt for either

• DDoS attack Prevention scheme for the loaded and process/memory intensive personalized pages.
• Large number of requests (same outgoing IP for large number of users) from same originating IP automatically getting blacklisted.

Providing the Google’s intelligent Bayesian filtering and intrusion detection algorithms in place, a CAPTCHA attempt looked a bit out of place to me, or probably it was just me.

References

CAPTHA is the squiggly characters / security code one encounters during signups and other online activities to keep bots away. It an acronym for "completely automated public Turing test to tell computers and humans apart") and is a type of challenge-response test used in computing to determine whether or not the user is human.

Spy Blog: Stupid Google virus/spyware captcha page
15 Seconds : Fighting Spambots with .NET and AI –Adnan Masood