Even if a key works, it is likely a "leaked" volume license. Once ESET’s servers detect that a single key is being used by hundreds of people across the globe, they blacklist it, leaving your computer unprotected without warning.
Many sites or posts offering these keys are "malware traps" designed to trick users into clicking malicious links or downloading "key generators" that contain trojans. Privacy Risks: facebook eset internet security license key 2023