Question about VAC

I have only used T_T's hacks a few times and heard this for some people on reddit, "Basically they scan your computer memory (RAM) in search for signatures - if they notice one, they will mark your account for delayed ban (from 30 minutes to months). After that period time they will mass ban all selected accounts - and that is when ban wave happens"
and
"Hacks need to be detectable first before they can ban people for using them. Every so often they catch a new cheat and can start scanning clients for signatures of that cheat, think breadcrumbs or leftover code that lets the person doing the scanning know that this player was cheating.So basically they do this in "waves" to catch as many hackers as possible. This is basically unrelated to the recent "pro" or "semi pro/amateur" bans"

What I am wondering is if anything they are saying is true? If it is, then none of us are safe.