https://www.bleepingcomputer.com/news/security/trickbot-malware-mistakenly-warns-victims-that-they-are-infected/

The notorious TrickBot malware mistakenly left a test module that is warning victims that they are infected and should contact their administrator.

TrickBot is a malware infection that is commonly distributed via malicious spam emails. When installed, the malware will run quietly on a victim's machine while it downloads various modules that perform different tasks on the infected computer.