According to BusinessWeek, over 99% of all the pings and updates pouring into Technorati’s servers come from spam blogs.
Technorati CEO, David Sifry’s take: “All healthy ecosystems have parasites.”
Wikipedia’s definition of spam blog:
Spam blogs, sometimes referred to by the neologism splogs, are artificially created weblog sites which the author uses to promote affiliated websites or to increase the search engine rankings of associated sites. The purpose of a splog can be to increase the PageRank or backlink portfolio of affiliate websites, to artificially inflate paid ad impressions from visitors, and/or use the blog as a link outlet to get new sites indexed. Spam blogs are usually a type of scraper site, where content is often either inauthentic text or merely stolen (see blog scraping) from other websites. These blogs usually contain a high number of links to sites associated with the splog creator which are often disreputable or otherwise useless websites.