"We pushed out a change that will prompt some users to solve a CAPTCHA if our spam classifier identifies the blog as spammy," wrote Google's Blogger Product Manager, Jason Goldman, on Blogger Buzz. "So far, we have observed a slight decrease in the amount of spam being created." The "CAPTCHA" test is a method by which automated programs that post or create blogs can be foiled--where the user is asked to type in a sequence of letters from a line that people can read, but computers can't decipher.

Spam blogs generally fall into one of two categories: Link farms, which pack hundreds or even thousands of blogs with gibberish or recycled content, and contain multiple links to a particular Web site, which allow them to game Google's PageRank algorithm, creating artificially high organic search rankings; and spam blogs that simply recycle content with AdSense or other advertising on them in the hopes of making money from errant users clicking on the ads.

Pete Blackshaw, chief marketing officer of Intelliseek, a firm that monitors and searches blog content, said that spam blogs--especially on Blogger--present a major problem for the corporate blogosphere. "We predict 30 percent of all the new blogs are spam-oriented," he said. "To some extent, it risks killing the bloom. It's hard enough to convince companies to blog, and spam blogs are giving them a really easy out: 'why would I want to deal with this?'

Blackshaw also said that spam blogs pose a threat to major brand names as well--certain popular brands or even Hollywood celebrities can find their names being exploited to drive traffic to spam blogs. "Most brands have no idea that they're being used as bait, but that's a taint on the brand--no brand wants to be associated with garbage," he said. "We might start to see some brands raise some tough questions about how they're used in these spam blogs in the same way that tough questions have been raised about buying certain keywords on Google," he said, referring to the Google-Geico lawsuit in which the search giant was accused of profiting by allowing competing advertisers to buy Geico's name as a keyword ad.

David Sifry, CEO and founder of blog search engine Technorati, had a much lower estimate of the percentage of blogs that were spam--2 to 8 percent--but said that spam blogs were an inevitable feature of the blogosphere. "Every health ecosystem has parasites," he said. "The really big question here, though, is--is it manageable?"

He added that major search engines, blog search engines, and net advertisers have begun working together to eliminate the economic incentive for spam blogging by identifying spam blogs at the source and simply not indexing them. "In the case of Web spam--and the reason I'm so much more optimistic about it than e-mail spam--is that in the end, it's all about accountability," he said. "The difference with Web is that in the end, every single thing on the Web has a URL. If you see one domain that's sending a lot of suspicious content, you can stop it right there at the source."

Sifry took a wait-and-see attitude toward Blogger's most recent move to cut down on spam blogs, but said that excessive measures to curb spam could damage the freedom inherent to the blogosphere. "This is a larger issue of how can you deal with the fact that you've built an open system," he said. "We want to make it easy to let people create content--but still enforce a good level of accountability and reputation."

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