Valve has banned roughly 90,000 Steam accounts following the Steam Summer Sale. The accounts were likely used for cheating.
The bans originate from the Valve Anti Cheat system, which is used in several popular Valve games, including Counter-Strike: Global Offensive and Dota 2, to prevent cheaters from ruining online experiences.
The statistics are available on various Steam tracking websites and gives insight in the number of players banned each day. The ban wave after last year's Steam Summer Sale affected roughly 40,000 accounts.
Valve currently doesn't use IP addresses to track and flag other accounts also in control of players who have used cheats. This means that primary accounts will remain unaffected.