Over the weekend, pornographic images and videos began appearing on Google Groups pages, along with infectious malware.

"These pages push other porn pages for profit," said Alex Eckelberry, CEO of security company Sunbelt Software, in a blog post. "While not all of the redirects go to malware sites, we did observe some redirects to a site which ultimately pushes a fake codec trojan, which if installed, results in a VirusHeat infection."

Google Groups is a free, online discussion forum available to anyone with a Google Account. Google uses a Captcha challenge to prevent spammers from using automated methods to create and abuse new accounts.

But about a week ago, Websense, an Internet security company, said that spammers have had achieved a 20% success rate cracking Google's Captcha system.

It's possible the influx of porn spam is related. Sunbelt security researcher Adam Thomas said in an e-mail that it's likely that spammers are using bots to bypass Google's defenses.

Eckelberry said in an e-mail that this apparently automated spam assault on Google Groups appears to be new. "We've seen similar types of things with other Google services (Blogger, Pages), but I believe this is a fairly recent phenomenon," he said. "One assumes with absolutely zero cost in setup, and automated systems doing the work, it's probably quite profitable."

Google Groups are also being set up to promote spam blogs, or splogs, for certain search keywords. For example, the Google Group "air-conditioning--1" was set up to associate the search keywords "free auto info trouble shooting air conditioning" with the splog mctop10.info through a Web link. There are dozens, if not hundreds, of such bogus Google Groups pages.

Or at least there used to be. "We have removed the Google Groups and accounts in question for violating our Terms of Service," said a Google spokesperson via e-mail. "Google is committed to preventing spam and other forms of abuse on Google Groups. We encourage users to notify us of any issues."

Google declined to comment on the integrity of its Captcha system.