The Federation Against Copyright Theft (Fact) has attacked a number of blue chip companies accusing them of indirectly funding online piracy.

Fact reported on Monday that it had confirmed 33 ad networks - the systems that place adverts on websites - including Google's Adsense and Yahoo's Search Marketing, as placing adverts on sites guilty of facilitating the illegal sharing of copyrighted material.

The anti-copyright infringement group went on to report that the ad networks were placing the adverts of at least 83 companies on file-sharing sites. In its statement Fact specifically listed discovering adverts from BT, British Gas and Tesco on the sites. As noted by the anti-piracy groups, it may be the case that the companies listed were not aware that their adverts were being placed on file-sharing sites - it instead being a mistake made by the ad networks.

"It's not the advertisers who are to blame. Ad networks and publishers call the online ads into these sites. It's down to their media agencies and suppliers to recognise that there is a solution out there that would eradicate this issue. Make the suppliers accountable to their own networks through transparent accountability and Fact will not need to waste any more letter heads on this issue," said Anthony Rushton, co-founder of online video ad serving and verification firm Telemetry.

Fact's claims come in the midst of a heated global debate regarding internet copyright infringement and intellectual property theft. The debate peaked earlier in January after numerous groups and companies mounted an ongoing series of protests against the US' Stop Online Piracy (Sopa) and Protect Intellectual Property (Pipa) acts.

Though Sopa has now been shelved, the ferocity of the protests has in-turn caused numerous governments, companies and groups across the world to debate the best way to combat internet piracy. At the time of writing none of the companies listed in Fact's report had responded to the International Business Times UK's requests for comment.