In an unprecedented move all 14 German credit card companies have handed over customer transaction details to the police in an effort to identify child pornography users.

Saxony-Anhalt state interior minister Holger Hoevelmann told reporters at a press conference that the companies had screened over 22 million transactions across all their customers to identify those paying money to child pornography websites.

A total of 322 people have since been arrested in an operation codenamed 'Mikado'.

"We are grateful to the credit card firms that provided their assistance and found the 322 cases themselves," Hoevelmann told Reuters.

"As far as data protection regulations are concerned, everything was done according to the law. Potential criminals should be aware: we will catch them all."

The arrested people were identified by regular payments of €61 to a website based in the Philippines. The site was identified by a German investigative television show.

Most of them have pleaded guilty to the charges and around 10 per cent were repeat offenders. Hoevelmann said that most of them lived alone.

However, the case has raised serious privacy concerns. Germany has very strong privacy laws and there are fears over how the operation was conducted and who carried it out.

"The voluntary release of such data is highly questionable, for in Germany, in principle, dragnet searches are simply outsourced to private firms," said Hartmut Kilger, head of the DAV German lawyers association in an interview with Reutlinger General-Anzeiger newspaper.