Some 13 web forums, including a Yahoo user group, have been closed down following an investigation by the European Association Against Piracy (AEPOC).
The targeted websites were being used by pirates to distribute encryption-beating smart cards for pay TV channels, according to content protection firm and AEPOC member, Irdeto Access.
After being notified of the activity on the user group, Yahoo complied with AEPOC's request that the user group be deactivated, as did a dozen other websites.
Graham Kill, chief executive at Irdeto, said: "The message we are sending out to pirates today is that we will find them whatever activity they are undertaking and wherever they are pursuing it."
"Whatever the scale of their operation, we have given notice to local and international pirates that their illegal actions will not be tolerated," he added.
It is not the first time that Yahoo has been used to distribute pirated goods. A report compiled by the US Software and Information Association claimed in January that 91 per cent of applications on auction sites such as eBay and Yahoo are pirated, compared to 60 per cent a year ago.
Auction websites have also come under fire from the UK-based Business Software Alliance which issued a set of guidelines for web auctions to help prevent online sales of counterfeit material.
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