Banwaves were pioneered by Blizzard and a number of online-centric developers and distributors use the technique.
The general strategy:
>Have techs search for private and public hacks, be aware of what's out there both for patches, hypothesize on detection methods
>quietly develop countermeasures and detection, implement fringe countermeasures to bait out more ambitious/dedicated cheaters and scare off randoms
>wait silently for a major event you want to have clean, amass more exploit tweaks and data
>ban the everliving fuck out of everyone caught in the net and roll out all of the changes at once and hope no one else was playing the Game and that they won't lose it
Also, when you say
>15-30% of players are either hacking or griefing.
this is only counting players who get reported one or more times, which is not a fair sample of the whole population.