Session hijacking is a cyberattack where an attacker takes over a user's active session with a website or online service, often by stealing session cookies or tokens. This allows the attacker to impersonate the user, gaining unauthorized access to sensitive information or performing actions as if they were the legitimate user. Session hijacking can occur through various methods, such as network eavesdropping, cross-site scripting (XSS), or malware. Protecting against session hijacking involves using secure connections (HTTPS), regularly updating software, and implementing strong session management practices.