Home Security Necurs botnet spreading new strain of Windows ransomware

Necurs botnet spreading new strain of Windows ransomware

The Internet's biggest spam botnet Necurs has been spreading a strain of Windows ransomware known as Scarab over the last two days, security companies say.

Necurs has something in the range of five to six million infected hosts online monthly, according to F-Secure. Its service model has the entire infection chain, from spam emails with malicious malware downloader attachments, to hosting payloads on compromised websites.


The emails arrive with subject lines like "Scanned from (Lexmark/HP/Canon/Epson)”. The attachment is named as “image2017-11-23-(7 random digits).7z“ and contains a VBScript downloader that pulls down the Scarab ransomware.

Security firm Forcepoint said it had noticed about 12.5 million emails of this kind in six hours beginning at 7.30GMT on Thursday.

"Based on our telemetry, the majority of the traffic is being sent to the .com top-level domain. However, this was followed by region-specific TLDs for the United Kingdom, Australia, France and Germany," the company said.

F-Secure said the Scarab ransomware was relatively new and was observed last June, with its code being based on the open source “ransomware proof-of-concept” called HiddenTear.

The latest version has no change in filenames, but appends a new file extension to the encrypted files with “.[suupport@protonmail.com].scarab”.

The ransom note reads:


Forcepoint said that as with previous Necurs campaigns, the VBScript contained a number of references to Game of Thrones.

It said that the Scarab ransomware that was dropped had the file name sevnz.exe.

"Once installed it proceeds to encrypt files, adding the extension “.[suupport@protonmail.com].scarab” to affected files. A ransom note with the filename “IF YOU WANT TO GET ALL YOUR FILES BACK, PLEASE READ THIS.TXT” is dropped within each affected directory," the company said.

"The misspelling of 'support' is present in both the modified filenames and the ransom note, and is presumably a result of the availability of email addresses on the Protonmail service.

"Unusually, the note does not specify the amount being demanded, instead simply stating that "the price depends on how fast you write to us". This note is also automatically opened by the malware after execution."

Graphic: courtesy Forcepoint. Screenshot: courtesy F-Secure


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Sam Varghese

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A professional journalist with decades of experience, Sam for nine years used DOS and then Windows, which led him to start experimenting with GNU/Linux in 1998. Since then he has written widely about the use of both free and open source software, and the people behind the code. His personal blog is titled Irregular Expression.