Security experts are warning bloggers and Web site administrators that trackback spam is flooding legitimate sites with links to pornography.

Sophos, an antivirus and anti-spam company, reports that Newsbreak, a Filipino online news service, found more than 27,000 links to pornographic Web sites posted on its own Web site. According to an advisory posted by Sophos, Newsbreak was hit by a flood of spammers posting the links to the illicit Web sites. The Web site has since suspended the trackback feature, and users are being asked to log on before posting any comments.

The trackback technology is used to let blog authors know who has seen and linked to their postings. It also enables readers to easily locate Web postings related to the subject matter. The problem is that it's also easy to abuse, allowing spammers to connect themselves automatically via trackbacks to postings on legitimate blogs, in the hope of directing surfers to their own sites.

Trackback spams can overwhelm a blog server -- the technical equivalent to a distributed denial-of-service attack.

"Trackback and comment spam, like their cousin e-mail spam, are a real pain, and can hit newcomers to blogging, as well as established Web sites like Newsbreak," said Graham Cluley, senior technology consultant for Sophos, in a written statement. "No one wants to find their blog hammered with nuisance comments pointing to online drugstores, adult Web sites, or bogus financial advice. Not only will your blog then help boost the popularity of these unsavory sites, but you may also be in danger of damaging your reputation with Web visitors."

Sophos analysts explained that spammers use automated bots that meddle with legitimate blogs to either advertise goods or include links to Web sites in an attempt to boost their search engine rankings.

"Some bloggers have chosen to simply disable trackbacks because they have found the effort required to delete unwanted links has become too much of a burden," Cluley said. "It's not uncommon for bloggers to find the vast majority of the trackbacks they receive are from spammers. It's a shame that an innovative technology like trackback should be so widely abused."