Malware-infected porn continues to proliferate on Google Groups pages.

To demonstrate, Sunbelt Software CEO Alex Eckelberry strode purposefully through the RSA Conference exhibition hall Tuesday afternoon, toward a bank of computers set up for public use by conference attendees. From the Google Groups advanced search page, he entered the keywords "porn video" and restricted the search to the past three months.

The Google Groups search results listed 838,000 posts made between Jan. 9 and April 8 that fit the search criteria. Most of those pages, Eckelberry said, contain malware. To prove his point, he clicked through to several of the Google Groups pages hosting explicit videos. In each case, dialogue boxes popped up asking Eckelberry to agree to install phony media codecs that are actually malware.

"This is directly because of the CAPTCHA hack," Eckelberry said, noting that the conference computers could not be infected because they were completely locked down.

Certainly not every one of those hundreds of thousands of pages contains malware. The handful of top Google Groups search results Eckelberry tested were infected. (Really, there are only so many porn pages one can test for malware on a public computer at a security show.)

CAPTCHA stands for Completely Automated Public Turing Test to Tell Computers and Humans Apart. CAPTCHA images are used by online companies like Google, Microsoft, and Yahoo to ensure that those creating new accounts or posting comments or content online are individuals rather than spam bots. But increasingly, machines are able to decipher CAPTCHA images.

According to MessageLabs, the CAPTCHA systems used by Microsoft's Hotmail and Yahoo Mail were being regularly defeated last year. In late February and early March, security vendors Websense and MessageLabs, respectively, said that spammers had managed to achieve at least a 20% success rate in attempts to defeat Google's CAPTCHA system.

CAPTCHA systems can also be defeated, albeit at a slower rate, by offering inducements to people in low-wage markets to solve CAPTCHA challenges.

A Google spokesperson said that the company's security engineers continue to see significant human involvement in creating accounts for misuse.

Google continues to mount a vigorous defense of its properties, to protect both its users and its brand. Google's spokesperson noted that the company in February had closed a hole that allowed malicious users to construct a Google URL with an "I'm Feeling Lucky" redirection command that could send victims to malware sites. The question is whether a vigorous defense is enough.