Haven't heard of it yet but a ten-second google search resulted in success. MOSS seems to be an anti-cheat which got released in 2010 by Nohope92. Whoever he is, I haven't heard of him either. These pieces of information are based on nohope.eu which was the first result when I looked it up. It supports many games right now. You got an option to request your game to be added. It seems to be a cheat used in leagues.
Also it got some basic features.MOSS is the monitoring tool in use for ESL leagues, EMS and GO4 and has partnership with several external leagues.
Since I have no experience with it yet I can't help in detail when it comes to the Moss Checker (for the .zip files) and how Moss works in general. Automatic random screenshots
Unique PC identifier based on Hardware information
Capture games key files
Real time Processor Speed versus BIOS setup and box nominal speed
Game Exe SHA signature and start time
Ingame screenshot stored when PrtnScrn is pressed
Macros usage reported including Keys, timing and deviation and usage count
The Processes names, path and SHA2 listing at game start
Why do you ask?