It's not too often that Valve comes out swinging their big ban hammer, but yesterday was one such occasion. On the official Dota 2 blog, Valve revealed that they have recently permanently banned over 40,000 accounts that were caught using third-party software to cheat. Valve used the cheaters' access to information "that wasn't visible during normal gameplay" to confirm their suspicions and dish out some bans.
Valve says that they released a patch once they understood how these cheats were working. Here is what Valve says they did to catch the cheaters in the act:
This patch created a honeypot: a section of data inside the game client that would never be read during normal gameplay, but that could be read by these exploits. Each of the accounts banned today read from this "secret" area in the client, giving us extremely high confidence that every ban was well-deserved.
The Dota 2 developer says that fixing underlying issues that make cheats like these possible is a priority for the team.