Why perform a network vulnerability assessment or review?
because there are certain individuals that will take any weakness in your computers and networks (firewalls, switches) and exploit it to their own ends.
What can an enterprising evil hacker do? Minimally use your computers and networks that you have bought and paid for to attack other machines.
Besides using your resources, the evil hacker can steal your data, your customer information, anything that can be pieced together to be sold on the criminal market.
To give an example of hacker prowess and ingenuity: the Cap’n Crunch whistle for example There were these whistles in Cap’n Crunch cartons, and they happened to whistle at 2600Hz frequency
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Before the phone systems were run by digital computers, the analog systems could be fooled in giving unlimited calls (long distance etc) at payphones.
I know it is stealing and a bad ethical thing, but look at the pure “hacking” ingenuity of the action finding of a whistle in a box, using it in a payphone and then trying various methods to steal calls.
Today’s hackers are just as ingenious with many different types of attacks.