Tewksbury, Mass. — A Massachusetts police department has fallen victim to a scam in which hackers encrypt the department's files and demand a ransom to unlock them.

Tewksbury Chief Timothy Sheehan tells The Boston Globe he felt he had no choice but to pay the $500 demanded by the hackers, because no one, not even private experts, could unencrypt the infected files.

The hackers demanded payment in Bitcoin, and sent through Tor, making it almost impossible to track.

The attack was first reported by the Tewksbury Town Crier.

The so-called ransomware is usually downloaded onto a computer system through an email that appears legitimate, but contains a hyperlink that when clicked infects the recipient's computer.

The only way around the problem is to back up the data.

Departments around the country have fallen victim.