We had an experience this evening with DNS server settings where our website DAFC.net mysteriously changed.
This had the effect of taking our domain offline and pointing to an unsafe server.
We are not yet sure what happened but when using mxtoolbox.com we noticed that a completely different set of IP addresses were being used instead of those we had setup.
We use joker.com as our registrar and all the settings appeared correct yet using mxtoolbox said otherwise. The website DAFC.net itself was also pointing to the incorrect location.
We tried updating the DNS records in joker.com but still the pointers were wrong.
However, we noticed that we were using joker.com nameservers and, as we still had control, we reverted the DNS servers to our actual server.
Hey Presto, 5 minutes later our website became visible (well, almost). Access to the website was still hidden due to the cacheing nature of DNS servers but we are confident that within an hour or two all be restored.