The MITRE ATT&CK framework for ICS (Industrial Control Systems) details various tactics and techniques that may be used by adversaries. In the scenario described, the presence of unexpected firmware versions with a checksum that does not match the official vendor firmware indicates that the firmware has been modified. In the MITRE ATT&CK framework for ICS, this falls under the "Persistence" tactic, as it demonstrates an adversary's ability to maintain their foothold within the environment through unauthorized modification of device firmware.