Microsoft researchers say they've tracked down all those search engine spam pages to a small group of "rogue actors" acting in collaboration with advertisers, The Times' John Markoff reports.

The report is online here (PDF).

The researchers uncovered a complex scheme in which a small group, creating false doorway pages, works with operators of Web-based computers who profit by redirecting traffic passed from search engines in one direction and then sending advertisements acquired from syndicators in the opposite direction.

Surprisingly, the researchers noted that the vast bulk of the junk listings was created from just two Web hosting companies and that as many as 68 percent of the advertisements sampled were placed by just three advertising syndicators.

As suspected blog services are a huge reason for the explosion in the problem, and ironically, it's Google's own Blogger that is the most wide open to abuse.

The Microsoft research findings, based on a survey in October, also determined that much of the spam ad traffic was being funneled through the Internet addresses of just two Web-hosting companies.

Phillip Rosenthal, chief technology officer of one of the companies, ISPrime, an Internet services company based in New York, said the activity had been traced to a single customer and violated the company’s acceptable-use policy. He said the company’s relationship with the customer, whom he would not identify, had been severed after the company was notified about the Microsoft paper by a reporter.