In computer security world, peoples who want to cause some trouble for their fun or for their own commercial profit are called intruders.
Basically, intruders are of the following two types:
Now, let's describe briefly about the above two different types of intruders.
Active intruders are malicious.
Active intruders always want to make some unauthorized access to the other's system to change, modify, or sometime delete the data.
Passive intruders are less malicious than active one.
Passive intruders want to read the files they aren't authorized to read.