We noticed Steam was offline even though the internet was working fine. We restarted Steam only to discover the sign-in was not working.
We also had some issues signing in on the Steam website but eventually we were able to log-in.
Curiously the mobile app was not affected. Steam uses the mobile app for a security so that stolen account credentials are not able to be used.
We simply opened up Origin and played Battlefield while we awaited for Steam to come back to life.
Steam Status did not notice that there was any problems.
Steam is now back up after being down for about 10 hours or so.