According to the Associated Press, the data theft is believed to be the biggest breach of private information Greece has ever seen.
Police Tuesday told AP that the 35-year-old, whose name was not released, was found in possession of identity card details, tax numbers, vehicle license plate numbers, and home addresses.
The files appeared to include duplicate entries, which means the number of individuals affected could be lower, the wire report states. Greece has a population of around 10 million.
Police don't know yet how the man obtained the files or what he intended to do with them. 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 told AP.
The 35-year-old was tracked down through the Internet, and computer equipment seized from his house during a search, the wire report said.
A similar data theft was reported in Israel a year ago, when a government contractor stole files from the country's Population Registry, ultimately affecting the personal data of the entire population.
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