What do movie pirates look for in an illegal download? Something they can't get elsewhere. According to information collected by the website PiracyData.org, online pirates are drawn to films that aren't available for sale in any other digital format.

PiracyData.org is run by tech policy researchers at the Mercatus Center, a pro-market think tank at George Mason University. Matt Sherman, a New York-based software developer, and Jerry Brito, who runs the Mercatus Center's tech policy program, told The Washington Post they got the idea from watching a hearing in which copyright owners complained that online search portals such as Google don't work hard enough to stamp out piracy.

The data that Sherman and Brito have been collecting suggest that content providers could do more as well. The website matches the piracy data published by TorrentFreak, a popular hub for downloading movies and music, with information about the legal availability of movies. Each week the site takes TorrentFreak's list of the 10 most pirated movies and checks to see whether they're available for authorized download elsewhere.

The site launched the first week of October. Within five weeks, the pattern was clear. Of the 10 most pirated films for the first week of November, only four were available for online purchase, two were available for rent, and none was available for streaming. During the first five weeks of the site's operation, only 44 percent of the most pirated movies were legally available in a digital format. Only 18 percent were offered for rental or streaming.