Last night Gary blogged on A New Report on Estimating Link Spam. Gary explains that the "21 page (pdf) technical research paper from the Stanford InfoLab that takes a look at link spam." The paper was written by two folks at Yahoo and two at Stanford; Zoltan Gyongyi (Stanford), Pavel Berkhin (Yahoo), Hector Garcia-Molina (Stanford), Jan Pedersen (Yahoo).
Read Link Spam Detection Based on Mass Estimation if you dare. :)
Link spamming intends to mislead search engines and trigger an artificially high link-based ranking of specific target web pages. This paper introduces the concept of spam mass, a measure of the impact of link spamming on a page's ranking. We discuss how to estimate spam mass and how the estimates can help identifying pages that benefit significantly from link spamming. In our experiments on the host-level Yahoo! web graph we use spam mass estimates to successfully identify tens of thousands of instances of heavy-weight link spamming.
Forum discussion soon to be at this thread at Search Engine Watch Forums.