By Stephen Jessel in Paris

A French court has given a computer engineer a 10-month suspended prison sentence, after he demonstrated how to break the security systems of banks' credit cards.

The 36-year old engineer, Serge Humpich, had tried to sell the secret of his discovery to the banks, and was prosecuted after he carried out a demonstration in the presence of a legal officer to show that his technique did work.

Two years ago, Serge Humpich made the discovery criminals can only dream of - how to forge a bank and credit card that can defeat security measures put in place by the organisations that issue genuine cards.

He found a method that would enable him to withdraw the equivalent of more than $2,000 every 15 minutes.

A secret to sell

Mr. Humpich took his discovery to the Interbank organisation that oversees security for the 33 million main French credit cards, each with its own microchip, with the idea of selling his secret to it for a reported $150,000.

The organisation turned his representatives away, so Mr. Humpich carried out a controlled experiment.

Accompanied by a legal officer, he went to a machine that issues tickets for the Paris Metro and, using a doctored card, bought himself some tickets.

The banks then pounced and Mr Humpich found himself on trial for fraud and counterfeiting. The public prosecutor called for a $7,500 fine and a 2-year suspended prison sentence.

The court imposed a lighter sentence of 10 months suspended, and no fine.

Mr Humpich, who has lost his job and has few prospects says he does not understand the court's verdict and has plans to appeal.