Well that’s a good question and the answer is we do not, can not, know. Anyone who asks the question tends to get shouted down by people ridiculing the idea that people should be concerned about privacy and cyber security at all.
The few decent threads I’ve managed to dig up on this sheds some light at least. I think it is safe to assume two things about it, it uses the USN Journal to keep track of all changes done to files and folders on your hard drives and it sends SOME sort of data back to the developers of the anti-cheat program.
What is sent back and what they can or can’t do with it is unknown but largely pointless to quibble about. It’s spyware and you have to trust that there’s no one malicious or incompetent at the other end of it. Considering that ALL major companies providing online services have been breached at one time or another that’s really not a gamble an ant-cheat system should make on my opinion.
My personal take on it is that I probably already own more games than I will have the time to play in my life time and so I do not have to trust BDO or Tencent owned Riot with this sort of thing in order to play their games.