When a file is scanned, VirusScan compares it to known threats. VirusScan also uses heuristic techniques to detect unusual behavior. When a file cannot be matched to a known threat, but exhibits unusual and possibly threatening behavior, VirusScan utilizes Artemis technology to evaluate the threat of the unknown file. If the file is deemed unsafe, VirusScan will quarantine the file to protect your computer.
It necessarily need not to be a virus , but McAfee proactilvely tries to block those files which might posses the characteristics of a PUP (Potentially Unwanted Program). Potentially Unwanted Programs affect your privacy and security and moreover as you say it being a keylogger progams has advantages and disadvantages/threats. McAfee takes a step ahead and blocks its so that users who accidentally download these type of loggers over the internet are not exposed to internet threats.
McAfee Online Community Moderator