Web attackers use various methods to steal data including phishing emails, SQL injection, cross-site scripting (XSS), brute force password attacks, malware, man-in-the-middle attacks, outdated software exploitation, and insecure API integrations. Defense strategies include user education, multi-factor authentication, input validation, HTTPS implementation, regular software updates, secure coding practices, and proper API security. The stolen data often ends up on the dark web where it's sold for identity theft and further attacks.