WannaCry

Overview
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The WannaCry ransomware attack was a May 2017 worldwide cyberattack by the WannaCry[a] ransomware cryptoworm, which targeted computers running the Microsoft Windows operating system by encrypting data and demanding ransom payments in the Bitcoin cryptocurrency.

The attack began on Friday, 12 May 2017,[5] and within a day was reported to have infected more than 230,000 computers in over 150 countries.[6][7] Parts of the United Kingdom's National Health Service (NHS) were infected, causing it to run some services on an emergency-only basis during the attack,[8] Spain's Telefónica, FedEx and Deutsche Bahn were hit, along with many other countries and companies worldwide.[9][10][11] Shortly after the attack began, Marcus Hutchins, a 22-year-old web security researcher from North Devon in England then known as MalwareTech[12] discovered an effective kill switch by registering a domain name he found in the code of the ransomware. This greatly slowed the spread of the infection, effectively halting the initial outbreak on Monday, 15 May 2017, but new versions have since been detected that lack the kill switch.[13][14][15][16] Researchers have also found ways to recover data from infected machines under some circumstances.[17]