WannaCry, the ransomware attack that changed the history of cybersecurity

WannaCry was a 2017 global ransomware worm that exploited the SMBv1 vulnerability (CVE-2017-0144) via the EternalBlue exploit, autonomously propagating to encrypt files and infecting over 200,000 systems across more than 150 countries; an accidental "kill-switch" registration slowed its spread and investigations later linked the attack to the Lazarus Group, underscoring failures in patch management, network segmentation, and the risks of stockpiled offensive cyber tools.