The presence of files such as mimikatz.exe, mimidrv.sys, and mimilib.dll on a target server indicates prior compromise. Mimikatz is a well-known post-exploitation tool used for extracting plaintext passwords, hash dumps, PIN codes, and Kerberos tickets from memory. These files suggest that an attacker has previously gained access to the system and used Mimikatz for credential harvesting. This is a strong indicator of a prior security breach rather than tools used for password encryption or false positives.
Reference:
Mimikatz Usage and Detection
Understanding Indicators of Compromise