In IT and technology, hackers are defined as a person or group of people who penetrate other people's IT systems/computers without authorization and use the system for their own, often criminal, purposes.
They can have different goals and motivations, e.g. they steal user-related data or pass it on without authorization. Hacking can take the form of social engineering, hacking passwords, infiltrating malware, spying on emails or writing down keystrokes. This results in money being stolen, data being resold, files being deleted or personal information being accessed. There are different types of hackers, e.g: White Hat Hacker, Black Hat Hacker, Grey Hat Hacker or Ethical Hacker.
In that case, not all hackers (ethical hackers) pose a threat to the IT system. Nevertheless, hacking can be very dangerous, which is why IT security is a top priority in order to avoid legal consequences and other security risks.