Hackers use various methods to infiltrate users' systems. Denial of Service (DoS) attacks disrupt normal functioning by overwhelming the system. Drive-by downloads involve the automatic downloading of malicious software without user consent. Malware refers to malicious software designed to damage or gain unauthorized access, while malvertising uses online advertisements to spread malware. Phishing attacks trick users into revealing sensitive information, and password attacks aim to crack user passwords. All these methods are commonly used by hackers to compromise systems.