Hackers have security-related knowledge and develop malware. Their goal is to overcome security mechanisms to expose vulnerabilities. After overcoming security devices, they have access to networks, virtual machines and data files, but they do not access or modify them. Depending on their objectives, hackers are referred to as white-hat, grey-hat or black-hat hackers. White-hat hackers look for vulnerabilities in computers and computer networks and inform the relevant company about them. Their goal remains solely to uncover vulnerabilities in the security infrastructure. In addition, there are the grey-hat hackers, who uncover security vulnerabilities in systems but use them for their own benefit, for example by publicizing the vulnerabilities or by putting pressure on the company's management. The third group of hackers are the black-hat hackers. The activities of these hackers are aimed at doing harm. They damage or falsify data and programs.
Recommended countermeasures against hackers include regularly changing passwords, eliminating vulnerabilities in the system, disabling unused system services, using callback as a communication routine, monitoring service inputs, and using IDS ( intrusion detection system) systems.
Hackers, on the other hand, can also be booked for finding security vulnerabilities or creating penetration tests. For this purpose, there are special Wesites that offer Hacking as a Service( HaaS).