Data on the computer is no longer available or is encrypted.
Encryption Trojans (also known as blackmail Trojans) are a specific family of malicious software that encrypts files on the victim's computer and on connected network drives, rendering them unusable for the victim. The ransomware scene is continually expanding. The gateways for such encryption Trojans include in particular poorly secured systems and emails with attachments.
Encryption Trojans can cause considerable damage, especially if your data backups are also affected. In the event of such an incident, remain calm and act with caution.