Using the sophisticated Flame malware first developed to spy on and sabotage Iran’s nuclear program, US spymasters were able to gain almost unlimited access to the computers of senior French officials in the last days of former president Nicolas Sarkozy’s reign, alleges a story in French magazine l’Express.

The impact of this alleged attack is unknown, but experts on the Flame malware—believed to be the most sophisticated cyberweapon ever developed—say that compromised computers could have been used to record conversations via infected PCs’ microphones. Screenshots may also have been captured, and files could have been copied. According to France’s intelligence agency, quoted in the story, the resulting data were then routed through multiple servers on all five continents in order to hide the ultimate destination of the stolen data.

The initial incursion was an extremely simple, tried-and-true bit of social engineering. Staffers at the official residence of the president of France, the Palais de l’Elysée, were friended by hackers on Facebook, who were no doubt using fake identities. Later, those staffers were sent emails with a link to a fake copy of the login page for the intranet of the Elysée. Once they entered their credentials, hackers had usernames and passwords they could use to log in to the real system.

Having gained access to the computers of the presidential office, hackers then dropped a piece of malware that was a modified version of the original Flame worm. Once it’s behind a security firewall, Flame can jump to other PCs in a network, even if it has infected only a single machine. The personal files of Nicolas Sarkozy were not compromised, said the story, because the then-president did not use a networked PC.

Asked whether the US was behind the attack, US Secretary of Homeland Security Janet Napolitano wouldn’t confirm or deny the accusation, according to the story.

If true, it’s still unclear why an attack would be launched in May, just days before Sarkozy lost the presidential election to François Hollande. But it’s possible that, despite the US and France being close allies, the US would want to guarantee French cooperation during a transition. In addition, the Elysée plays a key role in signing contracts with foreign countries, including those in the Middle East, notes an anonymous source who spoke with l’Express.