A Belgian court on Monday fined Internet search engine Yahoo! 55,000 euros (69,300 dollars) for failing to hand over personal details of users suspected of committing fraud.
Daily fines of 10,000 euros (12,590 dollars) were to be added for non-compliance.
In an enquiry into fraud carried out by people using pseudonyms in Yahoo! email addresses, the prosecutor had called on Yahoo to provide the true identity of the suspected cyber criminals.
California-based Yahoo! refused, arguing that it was a US company and therefore such information would have to be requested through US authorities.
"We strongly disagree with the court's ruling," Yahoo! said in a statement.
"The United States and Belgium have a formal international treaty which the prosecutor should have followed to properly seek information from a US company."
Yahoo! is basing its defense on a Mutual Legal Assistance Treaty between Belgium and the United States.
The treaty is intended to "improve the effectiveness of judicial assistance" by having designated authorities, usually respective justice departments, work out legal matters such as producing evidence across borders, according to the US Department of State website.
The public prosecutor responded that Yahoo! was also a Belgian company as its services are available in Belgium, stressing that there had never been such problems with American rivals Google and Microsoft.
The court in the northern town of Termonde imposed the 55,000 euro fine for "refusal to collaborate" with the judicial procedure, adding it would cost Yahoo! a further 10,000 euros per day in fines if it maintains its refusal to hand over the user data sought.
Yahoo! plans an immediate appeal based on the grounds the court does not have jurisdiction over the California firm's US operations and the prosecutor is dodging an international treaty crafted to deal with such cases.
The prosecutor in the Belgian criminal case skipped the MLAT legal process and had the court directly order Yahoo! to hand over private information sought as potential evidence, according to the Internet pioneer.
"Yahoo! is not withholding information from the Belgium government," the company said.
"We have a legal and policy basis for not disclosing information. We have raised this issue with the US government."
Yahoo! was denigrated by US lawmakers in 2007 for providing the Chinese government with email and other information that led to the imprisonment of two men that had advocated online for democracy in the Communist country.
Yahoo! settled a lawsuit filed against it by the Chinese men and their families in US federal court.
(c) 2009 AFP
Explore further: Japan court orders Facebook to reveal revenge porn IP addresses