Hackers are individuals with advanced knowledge of computer systems and networks. The term "hacker" can have both positive and negative connotations.

1. **White Hat Hackers:** Also known as ethical hackers, they use their skills to identify and fix security vulnerabilities. They often work to strengthen the security of systems, networks, and applications.

2. **Black Hat Hackers:** These individuals engage in unauthorized activities with malicious intent. They may exploit vulnerabilities for personal gain, to cause harm, or for other malicious purposes.

3. **Grey Hat Hackers:** This group falls in between, sometimes breaking into systems without authorization but without malicious intent. They may expose vulnerabilities to the system owner without causing damage.

It's important to note that "hacking" itself is a neutral term, and the context in which it is used determines whether it refers to ethical or malicious activities. Unauthorized access to computer systems is generally illegal and unethical. Ethical hacking, conducted with proper authorization and for security improvement, is a legitimate and valuable practice.