Spammers still defeating CAPTCHAS

Spam at Gmail doubled in past month, security vendor says

Spam originating from Google Inc.'s Gmail domain doubled last month, indicating that spammers are still defeating the CAPTCHA, the distorted text used as a security test to thwart mass registration of e-mail accounts and other Web site abuse.

Gmail spam went from 1.3% of all spam e-mail to 2.6% in February, according to data released today by e-mail security vendor MessageLabs Ltd.

The new statistics are another nail in the coffin for CAPTCHA, which stands for Completely Automated Public Turing Test to Tell Computers and Humans Apart.

Google is the latest free Web mail provider to fall victim to spammers who create software to determine the codes or sometimes employ people to solve the codes en masse.

"It's only a matter of time before [CAPTCHAs] are comprehensively defeated," said Paul Wood, a senior analyst at MessageLabs.

Last month, security vendor Websense Inc. ascertained that spammers were using two hosts to crack Gmail's CAPTCHAs. The method appeared to be successful only 20% of the time. But if the procedure is repeated thousands of times, many new accounts can be generated and used to send spam.

Most of the messages use links and images to advertise adult entertainment sites, Wood said.

While other spam domains can simply be blocked by antispam software, businesses are reluctant to cut off the domains of free Web mail providers because of their legitimate use, he said. Spam from Web mail providers accounts for 4.2% of all spam.

Google's CAPTCHA system is considered hard to crack, but so was Yahoo Inc.'s, which is also regularly beaten. MessageLabs said 88.7% of the spam from free Web mail providers comes from Yahoo's domains.

Microsoft Corp.'s CAPTCHA, used for registering accounts on its Windows Live Mail service, has also been cracked. Websense believes that the same group of spammers are responsible for breaking both Google's and Microsoft's systems.

Wood said MessageLabs provides Google and other companies with data that helps fight spam. Google could not be reached for comment.

MessageLabs sells a security service that filters e-mail before passing it to its 17,000 corporate customers. The vendor snags 2.5 billion spam messages per day from a total of more than 3 billion messages.

Copyright © 2008 IDG Communications, Inc.

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