Ransomware is computer code that alters or encrypts files on computers and servers. Once the files are locked, the hackers demand a payment, usually in bitcoin, before they will turn over a digital key that unlocks the files.
City officials in Plainfield, NJ, were told to pay the bitcoin equivalent of 650 euros to get their files back. When the officials called in police instead, the hackers stopped communicating.
Ransomware can take many different forms and security specialists and software developers are scrambling to keep up with many iterations. One example is the Cerber ransomware that adds the extension CERBER to every file that the program encrypts.
An article posted by SureShot Software describes how the Cerber virus works and suggests a number of ways to deal with an infection and offers links to programs that will scan for malware.