Cheating is a problem in an awful lot of online games, and Playerunknown's Battlegrounds is no exception. It's a fairly common complaint among the PUBG community that the developers aren't doing enough to combat cheaters, but numbers assembled by redditor sjk045 indicate that a whopping 13 million accounts have been permanently banned over the past 69 weeks.
The figure is based on weekly reports posted by Bluehole on the official Korean PUBG Cafe, indicating the number of cheaters banned that week. The banhammer swings gently at first—the first week saw 1,852 accounts banned, 1,294 accounts were taken out in week two—but it ramps up fairly quickly: 132,676 bans were handed out in week 32, and more than 1 million accounts were banned in week 42.
Sjk045 clarified that the numbers represent accounts banned, not people—the great likelihood is that at least some of the banned accounts belong to repeat offenders—and that they do not include temporary bans. "It clearly says that these are number of 영구 이용 정지 (which literally means Permanent Ban in Korean)," they wrote.
The bans have tailed off dramatically over the past six months, and the most recently tallied week dipped under 100,000 bans for the first time in almost a year. But as sjk045 points out, that doesn't necessarily indicate reflect the effectiveness of PUBG Corp's efforts because the number of PUBG players has also dropped significantly, from an average concurrent player count of nearly 1.6 million (and a peak of 3.2 million) in January to 535,000 (1.1 million peak) in the past 30 days.
I've reached out to PUBG Corp for confirmation of the figure, and will update if I receive a reply.