If you are one of the many who currently use Steam’s family sharing beta program, just a quick heads up as there is now a second layer of authorization that you must use.  Before all you needed to do was authorize the PC you would like your library available on.  The latest client beta goes one step further and asks you to authorize the account as well.  Here is all the info you need from the presser:

We’ve made a change to the way Family Sharing works in the most recent Steam client beta, where lenders must now identify the Steam users who may access and play their shared games on shared computers. This allows lenders more control while reducing the risk of VAC or other bans resulting from an unknown user accessing and abusing shared games on an authorized machine. 

Family Sharing is now a two-factor authorization process, where up to ten Steam accounts on up to ten machines may be authorized to share your library at a given time. Any of these ten users may log into any of your ten authorized machines to access and play your shared games. Additionally, users may still request access to your shared library by sending you a request from any machine where you’ve installed games. 

To authorize up to ten family members to share your games, visit Family Sharing settings using the most recent Steam client beta update. Our FAQ have also been updated to reflect these changes.