They wrote a script that impersonated users trying to access Facebook, and downloaded hundreds of thousands of possible CAPTCHA challenges from reCAPTCHA. They identified the file ID of each CAPTCHA challenge and created a database of CAPTCHA “answers” to correspond to each ID. The bot would then identify the file ID of a challenge at Ticketmaster and feed back the corresponding answer. The bot also mimicked human behavior by occasionally making mistakes in typing the answer, the authorities said.
I guess you can break systems like CAPTCHA if want it bad enough.