Equifax (2017)

Equifax's 2017 breach is the most costly privacy violation in history, with an unpatched Apache Struts vulnerability exposing Social Security numbers, birth dates, addresses, and credit card details of 147 million Americans. The resulting $575 million FTC settlement is a $75 million increase over the previous largest GDPR fine at the time. Beyond the financial penalty, the incident led to criminal indictments of four Chinese military officers, demonstrating that international cybercrime can carry serious consequences. The scale and resolution of this breach set a benchmark that no other incident on this list has surpassed.