The creators of the widespread Locky ransomware have added a fallback mechanism in the latest version of their program for situations where the malware can't reach their command-and-control servers.
Calling home to a server is important for ransomware programs that use public key cryptography. In fact, if they're unable to report back to a server after they infect a new computer, most such programs don't start encrypting files.
The good news is that Locky will start encrypting files using a predefined public key that's the same for all offline victims. This means that if someone pays the ransom and obtains the private key, that key will work for all other offline victims as well.
New Locky ransomware version can operate in offline mode | PCWorld