Steam's Christmas cache error in a nutshell

Mere hours ago it was reported by various sources including NeoGAF, Reddit and many other message boards that there was a massive error going around with Steam. This error allowed users to view and access the accounts of other Steam users. This included access to payment history, game libraries and phone numbers. This issue has been resolved at the time of writing, but before then, Steam’s various site outlets were online for a fair while.

Users were advised to not login or go to the Steam related sites in order to change details or check for damages. This would increase activity and interaction and thus created other entry points for users to stumble upon their accounts. Fortunately the Steam sites were placed offline after this error was discovered.

According to the very limited official notice from Steam staff, a Steam Community Manager sent out notice regarding the Steam issue:

Account information incorrect

We’ve gotten reports that people sometimes see other people’s account information on the account page. Valve has been made aware of this and are working on a fix.

Some frequently asked questions:
– No, Steam is not hacked
– Creditcard info and phone numbers are, as required by law, censored and not visible to users

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.

25 Dec 2015, 23:16 GMT: The issue now appears to have been resolved, and the Steam Store is back online.