While it was unclear what was going on, Valve was quick to shut the store to avoid unauthorized access.
Within a few hours, the store was back and everything was back to normal. Added Valve: "Steam is back up and running without any known issues. As a result of a configuration change earlier today, a caching issue allowed some users to randomly see pages generated for other users for a period of less than an hour. This issue has since been resolved. We believe no unauthorized actions were allowed on accounts beyond the viewing of cached page information and no additional action is required by users."
Written by: Andre Yoskowitz @ 26 Dec 2015 21:35