Some users have received emails with malicious attachments that try to encrypt all files/directories that the user has rights to. In most cases it is not possible to decrypt files unless paying a “ransom” to the author of the malware program. Basically it is possible to recover from this kind of situation only by restoring files from backups. These kind of viruses are usually called ransomware.
Messages are often disguised as invoices they contain for example a zip file with the virus and opening them activates the virus.
General advice for all users:
Anti-virus Applications are not bulletproof, so do not open suspicious emails and in particular their attachments. Delete them immediately!