Valve announced a change for Steam today that will make things a lot clearer for everyone, as developers will now need to clearly list the kernel-level anti-cheat used on Steam store pages.
Now if only they could more clearly communicate when games are playable offline.
Eli5: your PC has different access levels a program can run at. This prevents a malicious or badly coded program from completely fucking your computer. Kernel level anti cheat runs at the lowest level access that exists under windows. It can do basically whatever it wants to your PC, and if a backdoor is coded in (happens way more than you'd think), it gives malware basically total access to your PC.