After weekly maintenance Valve shipped a bug that made private Steam achievement lists public. Aggregators such as Exophase and SteamDB ingested them. Exophase owner Mike Bendel called it a Valve API error, not a hack. Unnamed apps showed up as AppIDs.

Named so far: Fable, Persona 6, Kingdom Hearts 4, Control Resonant, Gears of War: E-Day, Clutch, Horizon Hunters Gathering, Ace Combat 8, Metro 2039, Star Wars: Galactic Racer, Stranger Than Heaven, Rayman Legends: Retold, Tomb Raider: Legacy of Atlantis.

This is not the 12TB Steam2 dump. Valve has not commented. GamesIndustry.biz asked.

Source: GamesIndustry.biz