The malware then displayed a message which offered to decrypt the data if a payment (through either bitcoin or a pre-paid cash voucher) was made by a stated deadline, and it threatened to delete the private key if the deadline passes. When activated, the malware encrypted certain types of files stored on local and mounted network drives using RSA public-key cryptography, with the private key stored only on the malware's control servers. It propagated via infected email attachments, and via an existing Gameover ZeuS botnet. The attack utilized a trojan that targeted computers running Microsoft Windows, and was believed to have first been posted to the Internet on 5 September 2013.

The CryptoLocker ransomware attack was a cyberattack using the CryptoLocker ransomware that occurred from 5 September 2013 to late May 2014. For other similar software, some using the CryptoLocker name, see Ransomware § Encrypting ransomware. This article is about specific ransomware software called CryptoLocker.

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