that is a bad Christmas present. The Mars encryption is a ransomware.
Most important is, to clear ALL your devices (PC,s, phones, tablets etc) with a good antivirus (Bitdefender or the like), otherwise you may be infected again, or infect others. Disconnect all from the internet/your lan that is not cleaned.
make sure all your backups are safe, do not attach them to any device or it may encrypt the backups as well.
Most probable you have been infected via mails, attachments or even an intruder on the network. Make sure you cover all that asap to prevent re-infection.
As always: do not pay, format the device and restore your backups, once your lan is completely clean!
There are some tools that claim you can decrypt this, but no experience with this.