A Greek man has been arrested on suspicion of having stolen 9 million personal data files in what is believed to be the biggest breach of private information the country has ever seen.

Police said Tuesday that the 35-year-old, whose name was not released, was found in possession of the data files that included identity card details, tax numbers, vehicle license plate numbers and home addresses.

The files appeared to include duplicate entries, meaning the number of actual individuals affected could be lower. Greece has a population of around 10 million.

Authorities are investigating how the man, who faces felony charges of data theft, came into possession of the files and whether he intended to sell the list, police spokesman Christos Manouras said.

The investigation began Monday after an employee at the data protection authority notified police that someone appeared to have a large number of digital files containing personal data, the head of financial and electronic crimes police Dimitris Georgatzis said.

The 35-year-old was tracked down through the internet, and computer equipment seized from his house during a search, Georgatzis added.