This from a recently published academic study (summarized here):

"First and foremost, P2P game piracy is extraordinarily prevalent and geographically distributed [at least it was during the period analyzed]. However, the numbers in our investigation suggest that previously reported magnitudes in game piracy are too high," Drachen adds. "It also appears that some common myths are wrong, e.g. that it is only shooters that get pirated, as we see a lot of activity for children's and family games on BitTorrent for the period we investigated."