CAPTCHA project

CAPTCHA^TM tests have several applications for practical security, including (but not limited to):

Online Polls. In November 1999, http://www.slashdot.com released an online poll asking which was the best graduate school in computer science (a dangerous question to ask over the web!). As is the case with most online polls, IP addresses of voters were recorded in order to prevent single users from voting more than once. However, students at Carnegie Mellon found a way to stuff the ballots using programs that voted for CMU thousands of times. CMU's score started growing rapidly. The next day, students at MIT wrote their own program and the poll became a contest between voting "bots". MIT finished with 21,156 votes, Carnegie Mellon with 21,032 and every other school with less than 1,000. Can the result of any online poll be trusted? Not unless the poll requires that only humans can vote.

Free Email Services. Several companies (Yahoo!, Microsoft, etc.) offer free email services. Most of these suffer from a specific type of attack: "bots" that sign up for thousands of email accounts every minute. This situation can be improved by requiring users to prove they are human before they can get a free email account. Yahoo!, for instance, uses a CAPTCHA^TM test of our design to prevent bots from registering for accounts.

Search Engine Bots. It is sometimes desirable to keep webpages unindexed to prevent others from finding them easily. There is an html tag to prevent search engine bots from reading web pages. The tag, however, doesn't guarantee that bots won't read a web page; it only serves to say "no bots, please". Search engine bots, since they usually belong to large companies, respect web pages that don't want to allow them in. However, in order to truly guarantee that bots won't enter a web site, CAPTCHA^TM tests are needed.