In today’s digital age, data breaches pose a serious cybersecurity threat, exposing billions of records and causing significant financial and reputational damage. This study examines five major breaches—Equifax (147M), Yahoo (3B), Marriott (500M), Target (110M), and Uber (57M)—analyzing the attack methods, exploited vulnerabilities, and their impact. Common attack patterns included social engineering (Target, Yahoo), third-party vendor exploitation (Target, Marriott), cloud misconfigurations (Uber), credential theft (Yahoo, Uber, Equifax), and software vulnerabilities (Equifax, Capital One). The analysis found that weak authentication contributed to 60% of breaches, third-party risks to 40%, and poor encryption to 30%, compromising over 5 billion records, with 90% containing personally identifiable information (PII). Financial penalties exceeded $1.3 billion—$700M for Equifax, $148M for Uber, and $18.5M for Target—alongside severe reputational loss, including a $350M drop in Yahoo’s valuation. The findings emphasize the need for robust cybersecurity measures such as Zero Trust Architecture and Defense in Depth, along with real-time monitoring and threat intelligence. Promoting a security-aware culture is vital to mitigating future breaches and reducing financial risk.