When most people run a virus scan on their computer they have no idea exactly what it's looking for, or how it identifies a virus and what it does to 'clean' your computer of the effects of the malicious software. They don't need to. Some very clever security experts have created a program that does all of this for you.
The same is true when someone wants to hack into your computer. There is an abundance of software that experienced hackers and security experts have written to easily identify any vulnerabilities in your network, offer up 'payloads' such as ransomware, trojans, webshells, back doors etc that make your network a hacker's playground.
Hackers who use these tools blindly, with no idea of the technology behind it are called 'Script Kiddies'. They only know what the tools tell them and can easily be stopped by following standard security practices such as patching regularly, good security hygene and scanning your own systems for vulnerabilities (although many companies are lax at even doing this).
They are no where near as skilled as genuine hackers or cyber criminals who can quickly identify vulnerabilities in your system that tools or scans won't pick up. However, on the down side, they are far more numerous and most likely to be testing your defences.
So, for those readers playing hacker top trumps, scores below:
Script kiddies can do a lot of naive or unintentional damage, even managing to cause major data breaches, so do the security basics and keep them out!