WannaCry is a ransomware cryptoworm that first appeared in May 2017. It quickly spread across over 150 countries, affecting hundreds of thousands of computers. The ransomware exploited a vulnerability in Microsoft Windows to encrypt files on infected systems and demanded ransom payments in Bitcoin to decrypt them. The attack had a massive impact, particularly on healthcare services, including the UK's National Health Service, causing widespread disruption and financial loss. WannaCry highlighted significant cybersecurity vulnerabilities and the importance of keeping systems up to date.