Moving forward, the best defense is the : keep three copies of your data, on two different media types, with one copy kept entirely offline.
The is a malicious encryption program belonging to the STOP/Djvu family . When it infects a system, it locks personal files (documents, photos, and videos) and appends the .u2k extension to them. It then leaves a "_readme.txt" note demanding a ransom, typically $490 to $980, in exchange for a decryption tool. U2K ransomware [.u2k file virus] removal.
This is the most difficult part. There are two scenarios for STOP/Djvu variants: Moving forward, the best defense is the :