Quelle: The Second Eigenvalue of the Google MatrixSpam Detection. The eigenvectors corresponding to the second eigenvalue are an artifact of certain structures in the web graph. In particular, each pair of leaf nodes in the SCC graph for the chain + corresponds to an eigenvector of C with eigenvalue 0. These leaf nodes in the SCC are those subgraphs in the web link graph which may have incoming edges, but have no edges to other components. Link spammers often generate such structures in attempts to hoard rank. Analysis of the nonprincipal eigenvectors of C may lead to strategies for combating link spam.
