Posted by Virus Bulletin on Feb 26, 2008
Twenty per cent success rate sufficient to create thousands of spam accounts.
Gmail has become the latest free webmail service to have its CAPTCHAs cracked by spammers.
Following the recent news of the Yahoo Mail and Windows Live Mail CAPTCHAs having been cracked, the news of Gmail's CAPTCHA being surpassed will come as little surprise.
Gmail, known as Google Mail in some countries, is the free webmail service offered by Google. Before being able to set up a new Gmail account, users are required to solve a CAPTCHA - which was believed to be very hard to crack - thus preventing automated registration of accounts.
However, using the combined forces of two hosts, spammers have managed to crack the Gmail CAPTCHAs with a success rate of one in five. As the registration attempts are carried out by bots in a botnet, this is a suffienctly high success rate to allow the attackers to create a large number of free accounts from which to send spam.
Researchers at security company Websense, who first discovered the attack, believe that it is being carried out by the same group behind the cracking of Windows Live Mail CAPTCHAs earlier this month.
Like both Windows Live Mail and Yahoo Mail, Gmail is a valuable resource for spammers - providing free access to powerful mailing resources, and with its broad popularity and large legitimate user base it provides a domain address that is unlikely to be blocked by spam filters - thus stepping up the challenge for spam- and malware-fighters.