The Grand Palais, which is hosting Olympic events in Paris, and around 40 other museums in France were victims of a ransomware attack at the weekend, police sources told AFP Monday.
Cybercriminals targeted the system used to "centralise financial data" for brands located at the various institutions on Saturday night, the source said.
The attackers had demanded a ransom and threatened to release financial data.
France's national cybersecurity agency ANSSI confirmed that it had been alerted about an "incident", adding that the hacked systems were not involved in the Olympic games.
The Grand Palais, which normally hosts major cultural exhibitions but is currently an Olympic venue for fencing and martial arts, confirmed it had been hit by a cyberattack but would not provide details.
After initially being mentioned as a possible target by the police source, the world-renowned Louvre denied being hit by the hacking.
According to the police source, a criminal investigation has been opened into attacks on data systems and for extortion by organised gang.
Ransomware generally involves hacking into computer systems and demanding money in exchange for unblocking them.
Source: AFP