France’s finance ministry was subject to a cyber attack in December targeting information related to its presidency of the Group of 20 nations.
Budget Minister Francois Baroin said the infiltration of some 150 computers did not seek access to any personal records or tax information contained in them.
"What was targeted, it seems, was the organisation of the G20," Baroin, who is also the government's spokesman, told Europe 1 radio.
The minister said officials had been shocked by the scale of the attack. "It is probably the first time it has been so spectacular," he said.
He added that there were some clues to the identity of the hackers, but he did not provide further details.
The website of Paris Match magazine (www.parismatch.com) quoted an unnamed senior ministry source as saying some of the information had been redirected towards Chinese websites but added that the source said this was not necessarily significant.
A source close to Finance Minister Christine Lagarde said he could not confirm or deny the magazine's report.
France began its G20 presidency in November with ambitious plans to tackle high commodities prices, reform the global monetary system and complete the G20's framework for tackling the global economic imbalances caused by some countries' large trade surpluses or government deficits.
It hosted a meeting of G20 finance ministers and central bank governors in the finance ministry last month, which agreed on a list of indicators to measure imbalances in the global economy, including trade balances and government deficits despite strong resistance from China.
Beijing managed to exclude real interest rates and levels of international reserves and G20 nations must now establish guidelines by April for using the list.
The source close to Lagarde said security services had taken immediate steps to stop the attacks when they were detected.
"We definitively finished (the job) last weekend," he said, adding that some 10,000 ministry computers had been protected.