Hacking refers to testing and securing networks and computers from vulnerabilities through ethical hacking practices like penetration testing and vulnerability assessment. Ethical hackers, also called white hats, help secure systems from unauthorized access by crackers, or bad guys, who break into systems for malicious reasons like destruction or theft. Maintaining system security requires constant updates, antivirus software, firewalls, and avoiding common attacks like denial of service, SQL injection, phishing, and ping of death attacks. The most secure system is one that is constantly patched and protected, as no system can be fully sealed from internet connectivity and threats.