Spammers create accounts at free mail services like Yahoo Mail or Gmail, but to make the process more efficient, they need to automatize it. The major challenge is that most web mail providers use CAPTCHAs ("Completely Automated Public Turing test to tell Computers and Humans Apart") and they are difficult to solve automatically. Last month, Websense Security Labs discovered that spammers managed to create bots that automatically sign up for new Gmail accounts with a success rate of 20%.
We discovered that the CAPTCHA breaking process for Gmail is sophisticated when compared to the Live Mail CAPTCHA break up which was reported in our recent blogs. It is observed that two separate hosts active on same domain are contacted during the entire process. These two hosts work collaboratively during the CAPTCHA break process. Unlike Live Mail CAPTCHA breaking, which involved just one botted host doing the entire job (signing up, filling in details, getting the CAPTCHA request), the Gmail signing process involves two botted hosts (or CAPTCHA breaking hosts).
Jeff Atwood thinks that "there's simply too much money to be made in email spam for the commercial CAPTCHA algorithms, regardless of how good they may be, to survive forever." He suggests to diversify the tests and use more difficult tasks like distinguishing dogs from cats or solving failed OCR inputs, but making the test more complicated will frustrate users.
Update: there's a program called Jiffy Gmail Creator that promises to automatically create Gmail accounts. "Normally, the average amount of time it takes to create a GMail account on a fast connection is approximately 4 minutes. With this software you can create a single account in under 10 seconds, and 10 accounts in under 2 minutes. Obviously this saves you loads of time," explains the site (I think you need less than a minute to create a Gmail account manually). The program costs $57, but I'm sure it's not the only one.