[en] Nessus licence

A while ago, a consultant from a competitor company launched a scan on a live network.
I don't know exactly what tool he used - Nessus or Nmap, I suspect. And I don't know what options he chose.
The main problem is that he probably did not know either.
As a result, the whole network crashed.

There should be a Nessus licence, just like there are driving licences.