Malware
surtr
According to PCrisk, Surtr is ransomware.
surtr is a Windows malware family.
Background
PCrisk classifies Surtr as ransomware. Threats of this kind encrypt and rename files before producing a ransom note. Surtr in particular adds the decryptmydata@mailfence.com email address and the ".SURT" extension to affected filenames.
Source: Malpedia (Fraunhofer FKIE).