The scourge of ransomware has exploded over the past 18 months, and local authorities, healthcare and police have all suffered outbreaks, as have hundreds of thousands of ordinary PC users.
Ransomware is a pernicious form of malware that encrypts files and demands payment, usually in bitcoin.
It's a far cry from the irritating Word Macro viruses that proliferated in the late 1990s as the internet was first becoming globally popular. However, the first encrypting ransomware, which went by the name of 'AIDS'*, was written in 1989 by Dr Joseph Popp, who was declared mentally unfit to stand trial.
However, it wasn't especially effective, nor was the floppy disk an especially effective medium for propagating it. The use of symmetric cryptography also rendered it somewhat ineffective as the decryption key could be extracted from the malware code.
Researchers Adam Young and Moti Yung introduced the idea of using public-key cryptography in 1996, and some form of electronic money was the ransom currency of choice.
This is probably why it wasn't until 2013 that the latest genre of ransomware emerged, after bitcoin had become firmly established.
Ransomware has evolved fast since 2013, and the number of attacks quintupled during 2016 alone. So which are the nastiest of this new strain of malware?
This is the ransomware that showed all the other cyber toe rags how to do it in 2013. The malware propagates via infected email attachments, encrypting particular classes of files stored locally and on mounted network drives using RSA public-key cryptography. The private key is stored on the malware's control servers, to which it connects when activated.
The malware displays a message offering decryption of the data if payment is made by a particular deadline, alongside a threat that the decryption key will be deleted if the user doesn't cough up in time. CryptoLocker can be removed, but the encrypted files will stay resolutely encrypted.
The Gameover ZeuS botnet network used to run CryptoLocker was taken down in an international operation in 2014 and the crypto analysed. As a result, an online tool is available to recover files encrypted under CryptoLocker. The scammers, however, laughed all the way to bank as they still got away with some $3m.
CryptoLocker spawned a number of imitations, including unpleasant clones such as CryptoWall and TorrentLocker. Above all, it provided the proof-of-concept for malware writers and other online ne'er do wells, who haven't looked back since.
* Dr Popp was a Harvard-trained anthropologist and consultant with the World Health Organisation in Kenya. He claimed that all the proceeds from the ransomware were being donated to research into HIV and AIDS.
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