Steam, the online market for PC games, experienced a major glitch on Friday.

Steam users who logged in were getting access to other users' accounts. We've also seen reports on social media that some people were able to make purchases with other users' credit cards.

In fact, simply visiting the Steam store website gave anyone access to another user's account.

Valve, the company that runs Steam, shut down the store within an hour after the glitch hit. The store was operational again about two hours later.

It's unclear what the cause was, and Valve's statement to The Verge didn't shed much light on what happened. Valve has only said the glitch was caused by an "internal error."

Meanwhile, the glitch put 125 million of Steam's active users at risk.

Think of Steam as the App Store for PC games. Users store their credit-card information and purchase games for download to their PC. A lot of that information was exposed in this glitch, and Valve hasn't said anything to assure its customers that everything is OK.