Valve went on a banning spree recently with close to 100,000 Steam accounts being banned in the span of just one week.
The ban wave appears to have quieted down now, but SteamDB's charts (via PCGamesN) show the banning carnage that took place just last week. Over the course of several days, Valve Anti-Cheat took action against tens of thousands of players in a series of bans that first started out in the thousands per day, a number that's consistent for VAC bans. The system watches over some of Steam's biggest games to keep cheaters out, Dota 2 and Counter-Strike: Global Offensive included among others. However, those numbers saw a huge spike on July 18 with 28,507 VAC bans occurring that day alone, a number coupled with 31,047 game bans.
That number of bans was already a big jump up from the typical range of daily bans, but it was dwarfed in comparison to the next day's total. On July 19, VAC banned 61,424 people from Steam with the game bans a bit lower than the day before at 27,402. This brings the total number of VAC bans during this month alone to 120,520, a number that's usually only reached at the end of each month if it even manages to get that high.
As PCGamesN pointed out, this appears to be the largest VAC ban wave that's ever been recorded in Steam's history. The exact cause of what triggered the series of bans isn't known, but it's assumed that the platform's anti-cheat software was able to find some sort of cheat that wasn't previously known about, one that a lot of Steam users were apparently using. Whatever that cheat was, the fact that it was found means that anyone who might not've gotten caught by the first wave may still feel the wrath of the VAC in the future.
As people who play fairly might expect, the cheaters aren't being sorely missed now that they're gone. In fact, there's an entire subreddit dedicated to the justice of banning Steam users that's had quite a bit of content to work with in the past week since the ban wave happened. If you've been slighted by a cheater and need some closure, you can head over to that part of Reddit to see evidence of accounts with hundreds of thousands of dollars worth of content now banned by VAC.