The detective agency used by the Motion Picture Association of America has attempted to lure file sharers to a fake download site that installs spyware on their PCs.
The MiiVi.com site offered downloads of complete movies along with forums for debate, but also offered software purporting to speed up file transfers.
In fact the software checked hard drives for copyrighted material and reported back to the MediaDefender detective agency.
"Unfortunately, with the site down, we cannot analyse the site or this tool, " said Carole Theriault, senior security consultant at Sophos.
"But if pirated software was made available for download and had some hidden processes that reported back to an unauthorised third party, it is a good thing that it is offline.
"This looks like a case of 'surfer beware' because pirated software is rarely without a sting in the tale.