Microsoft has been told by a US District Court that it must hand over e-mail details to an unnamed law enforcement agency, even though that data is held offshore.

In a case that will exacerbate concerns in non-American countries about the extra-territorial reach of US laws, a magistrate in the District Court of Southern New York, Judge James Francis has ruled that the tech giant “cannot refuse to turn over customer information and emails stored in other countries when issued a valid search warrant from U.S. law enforcement agencies,” according to Reuters.

The ruling will be a blow to Microsoft's attempts to assure non-US customers that their cloud data is safe from American spooks' demands for access. The company has criticised countries like Australia for policies that require government data to be stored locally: now, it will be fighting a ruling that extends US search warrants' reach into offshore data centres.

The judge's reasoning is based on an efficiency argument: if Microsoft isn't obliged to hand over the information the warrant seeks, the unnamed US law enforcers seeking the identity of (and other information about) the unnamed target of the warrant would have to coordinate with bodies in other countries (in this case, Ireland, since the data is held in Dublin).

A requirement for such coordination would mean that “the burden on the government would be substantial, and law enforcement efforts would be seriously impeded”, Judge Francis stated. He also ruled that the US Stored Communications Act is not bound by the same law as restricts search warrants to US territory, since the SCA covers digital communications.

That's because Judge Francis chose to treat the warrant as the equivalent of a subpoena, in which documents demanded by the court must be produced, no matter where they're held.

Microsoft has responded by saying that customer data outside America shouldn't be subject to search and seizure by US authorities, and is seeking a review of the decision. Reuters says a Microsoft statement says “A US prosecutor cannot obtain a U.S. warrant to search someone's home located in another country, just as another country's prosecutor cannot obtain a court order in her home country to conduct a search in the United States. We think the same rules should apply in the online world, but the government disagrees.” ®