A Security Consultant Is Analyzing Data from a Recent Compromise

A security consultant is analyzing data from a recent compromise. The following data points are documented: Access to data on share drives and certain networked hosts was lost after an employee logged in to an interactive session as a privileged user. The data was unreadable by any known commercial software. The issue spread through the enterprise via SMB only when certain users accessed data. Removal instructions were not available from any major antivirus vendor. Which of the following types of malware is this an example of?

A) RAT
B) Ransomware
C) Backdoor
D) Keylogger
E) Worm