This seems to be a big problem, maybe a virus. I had this first on saturday happening to my MacBook Pro 2015, then it happened on today to my MacMini and seems to be happening to my older MacBook 2011. Symptoms are these:
1) Internet connection stops working
2) while you try to trouble shoot, you will see your Admin account does not work any more
3) You try to open up terminal only to find out it does not work
4) You try to reboot and then you will see you mac won't boot up any more, you will get the text
OSX FIPS Ingtegrity Test: The /var/db/FIPS/fips_data file does not exist (2)
FIPS USER Space POST: Integrity test failed!
FIPS_POST failed!
<Emergency>: Boot task failed: fips
<Emergency>: Shutting down in 3 seconds.
And your mac is gone.
I am still keeping my old MacBook Pro up as I don't want to shut it down.
I was able to save my data to an external hard disk but we do need a solution!