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Definition: WannaCry is a ransomware strain that spread rapidly across a large number of computer systems in May 2017. It encrypted files on affected Windows systems, demanding a ransom payment in Bitcoin for the decryption key.

The WannaCry ransomware outbreak was one of the largest and most notorious cyber attacks in history due to its scale, speed, and the vulnerability it exploited. It leveraged a vulnerability in Microsoft Windows’ Server Message Block (SMB) protocol, known as EternalBlue, which was believed to have been developed by the U.S. National Security Agency and later leaked by the hacker group called The Shadow Brokers.

WannaCry’s impact was global, affecting organisations across various sectors, including healthcare (notably the UK’s National Health Service), finance, telecommunications, and more. This attack highlighted the importance of regular system updates, as Microsoft had released a patch for the vulnerability before the attack spread but many systems had not yet applied it. The outbreak triggered widespread awareness around cyber security practices and the importance of protecting against ransomware.

Key Characteristics:

  • Ransomware: A type of malware that encrypts files and demands a ransom for their decryption.
  • Exploited EternalBlue Vulnerability: Utilised a known Windows vulnerability for which a patch was available but not widely implemented.
  • Widespread Impact: Caused considerable disruption globally, affecting systems in over 150 countries.
  • Prompted Security Enhancements: Led to increased attention and improvements in cyber security and ransomware prevention.


  • Real-World Example: With WannaCry, numerous UK National Health Service trusts were infected, resulting in disrupted healthcare services and cancelled appointments.
  • Hypothetical Scenario: A medium-sized business with outdated operating systems becomes infected with WannaCry, leading to encrypted files and halted operations until the ransom is paid or backups are used to restore data.

Related Terms:

  • Ransomware: Malware that encrypts data and demands payment for the decryption key.
  • EternalBlue: The name of the exploit used by WannaCry, which targeted a vulnerability in the Windows SMB protocol.
  • Patch Management: The process of managing and applying software updates to systems to prevent exploitation by malware like WannaCry.

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