Malware
rarstar
This ransomware encrypts all user’s data on the PC (photos, documents, excel tables, music, videos, etc), adds its specific extension to every file, and creates the HOW_TO_DECYPHER_FILES.txt files in
rarstar is a Windows malware family operated by Tick.
Background
This ransomware encrypts the full range of a victim's files (photos, documents, Excel spreadsheets, music, videos, and so on), appends its own extension to each one, and drops a HOW_TO_DECYPHER_FILES.txt note in every directory that holds encrypted files.
Source: Malpedia (Fraunhofer FKIE).