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Thursday, 19 September 2019 08:28

Windows ransomware WannaCry still spreading, but the kick has gone


The infamous ransomware WannaCry, which burst on to the world stage in May 2017, is still very much alive and infecting Windows PCs, but a zipped portion appears to have gotten corrupted, preventing its encryption and ransom note creation components from working.

Noting this, the security firm Sophos said in a detailed paper released on Wednesday that unpatched Windows PCs were still providing a welcome for WannaCry which was crafted using the leaked NSA exploit, EternalBlue.

Sophos researchers Peter Mackenzie, Fraser Howard and Anton Kalinin said that more than 12,000 variants of what is arguably the most famous ransomware had been discovered.

WannaCry was stopped in its tracks when British security researcher Marcus Hutchins registered a domain he had found in its source code; the malware had been programmed to check this domain, and continue spreading if it could not access the domain.

The Sophos trio said that more than five million WannaCry attacks had been blocked in the last three months of 2018, as detected by the company's software.

They also found that about 97% of the Windows PCs that came under attack were running Windows 7, adding "so this is not just a story about forgotten Windows XP devices".

kevin wannacry tweet

WannaCry has three elements – the worm part which enables it to spread without any vector, the kill switch, and the ransomware part which is a zipped archive.

Many of the variants that were encountered by the Sophos researchers had the kill switch disabled and skipped over to the last part of the ransomware. But as the zipped archive had been corrupted, the expected function did not run to completion, something mentioned by British security researcher Kevin Beaumont.

Mackenzie, Howard and Kalinin said that this behaviour had been noted as early as two days after the initial breakout — 12 May 2017 — with French researcher Matt Suiche confirming this from a sample that had been uploaded to the virus database VirusTotal by Kaspersky staffers.

"The MD5 hash of the file uploaded to VirusTotal, which doesn’t have a kill switch and doesn’t encrypt files, is none other than the exact same file we now see causing the highest number of WannaCry detections: MD5: d724d8cc6420f06e8a48752f0da11c66," the Sophos team wrote.

"It is number one on the of unique file variants list provided earlier, causing 29% of all WannaCry detections in our data.

"Even more amazing is that the top three files on our list are all variants of this same file. The other two files contain the same corrupt archive; the only difference is in how the kill switch has been removed."


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Sam Varghese

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Sam Varghese has been writing for iTWire since 2006, a year after the site came into existence. For nearly a decade thereafter, he wrote mostly about free and open source software, based on his own use of this genre of software. Since May 2016, he has been writing across many areas of technology. He has been a journalist for nearly 40 years in India (Indian Express and Deccan Herald), the UAE (Khaleej Times) and Australia (Daily Commercial News (now defunct) and The Age). His personal blog is titled Irregular Expression.



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