Microsoft has started a pilot program to expand its adCenter contextual advertising network, similar to Google’s AdSense and Yahoo’s publisher network, to smaller publishers. Microsoft told CNET News the program began earlier this year and that “Microsoft’s self-serve advertising offering for publishers is still under development and is currently in a private pilot phase, being tested by select publishers who met the participation requirement.” Microsoft already places contextual advertising on large publishers including the Wall Street Journal and Rodale.