Music rightsholders have regularly criticised Google for its online ads popping up on websites devoted to piracy. Now they’ll have more ammunition in the form of an Advertising Transparency Report from the USC Annenberg Innovation Lab – the first of a planned monthly series examining which online ad networks are placing the most ads on pirate sites. What’s more, Yahoo is also in the frame.

The study actually draws on Google’s own Transparency Report data on DMCA takedown requests filed for its search engine. USC’s team is scraping the ad network identifiers on the sites with most takedown requests, then compiling a monthly chart of the top 10 ad networks placing ads on those sites. Openx takes top spot in the first chart, followed by Google, Exoclick, Sumotorrent, Propellerads, Yahoo, Quantcast, Media Shakers, Yesads and Infolinks.

The Lab’s director Jonathan Taplin reckons “the self-regulation of major sectors like the online advertising industry could make it harder for the Kim Dotcoms of the world to unfairly exploit artists”, although Google has responded sharply to the research: “To the extent [the study] suggests that Google ads are a major source of funds for major pirate sites, we believe it is mistaken,” a spokesperson told the Los Angeles Times. “Over the past several years, we’ve taken a leadership role in this fight.”

The idea of battling online piracy by squeezing the revenue streams for pirate sites has gained currency in recent years, including ad networks and payment companies like PayPal.

Google itself teamed up with PRS for Music for a study called “The Six Business Models of Copyright Infringement” exploring the importance of advertising to piracy sites. Here’s hoping the USC report sparks genuinely-constructive discussion about how this strategy should evolve, rather than just another stick for rightsholders to beat Google with.