An electrical engineer used the Internet to sell fake cards for decoding Dutch satellite television transmissions.

David Mainwaring, 34, of Buckingham Close, Didcot, was convicted of supplying goods for which a false trade description was supplied, selling an unauthorised decoder and advertising an unauthorised decoder for sale at Oxford Crown Court yesterday.

The jury took four hours to return a unanimous verdict against Mainwaring, who pleaded not guilty to the charges brought by Dutch broadcaster Canal.

Jonathan Goulding, prosecuting, said Canal+ hired a private investigation firm, Alternative Investigation Management, based in Maidstone, Kent, to scan the Internet for companies selling cards - known as Irdeto cards - that would descramble their satellite signal when inserted into a receiver.

AIM operative, Shabnam Shan found an online advert for Mainwaring's company, Prosat, offering to sell Irdeto cards capable of descrambling signals from nine broadcasters including Canal+.

Miss Shan called Mainwaring and offered to buy an Irdeto card from him for £139.

In a tape-recorded conversation with Miss Shan, Mainwaring said: "The reason why we can't take cheques is because it's illegal at the moment, you probably know that don't you."

Miss Shan visited Mainwaring's house and bought a Irdeto card from him.

Clive Sutton, defending, claimed Miss Shan bought a legal blank card from Mainwaring.

Mainwaring's company folded shortly before his arrest and Judge Peter Crawford took into account Mainwaring's financial hardship before fining him £500 for the offences.

Judge Crawford said: "I'm quite sure you knew from the start that it was illegal."