The department noticed a problem opening computer files Nov. 6 after opening an email attachment from what looked like a trusted source, The Boston Globe reported Tuesday.
Upon opening the attachment, a window popped up on the computer screen demanding the ransom in exchange for unlocking the files, Lt. Gregory Ryan said.
The CryptoLocker virus doesn't remove information from a computer, instead it makes it inaccessible until a ransom is paid within a set time period. If the ransom isn't paid by the end of the time frame, the files are locked forever, the Globe reported.
The police department contacted the FBI about the situation and made a "professional decision" to pay the ransom Nov. 9, Ryan said.
Ryan said information on the department's files wasn't compromised by the incident.
The department was looking into ways to better protect their computer system after the virus.