It was all fine this morning.
Nobody has touched it all day.
Tonight it is no longer passcode protected, I cannot open some TIO due to a parental lock 
being in place, I have to 'click' the touchpad rather than just touch it to click anything, all my past history is gone (bookmarks etc).
It's all backed up on an AirPort, so I am not too worried about content.
But what on earth happened?
Apparently my firewall is switched off. I cannot reset it because I have no clue what my administrator username and password might be. It does not seem to be my Apple password.
To say I am 
is an understatement…
Can anybody shed any light on this??