Home Security Necurs botnet now grabs telemetry data on Windows systems

Necurs botnet now grabs telemetry data on Windows systems

The Necurs email botnet has made a return and, apart from spreading new variants of the Locky ransomware and the Trickybot trojan, also has new functionality that gathers telemetry data from the Windows desktop of its victims.

Researchers at security firm Symantec said the new functionality included the ability to take screenshots and mail them back to a remote location.

There was also an error-reporting capability that reported back any errors that were encountered by the downloader as it tried to do what it was programmed to do.

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A typical invoice email sent by the Necurs botnet.

The new rash of emails from Necurs use the tried and trusted method of social engineering with a fake invoice as the lure.

If the file attached to the email was opened, then a JavaScript file was downloaded through an embedded iframe; the JavaScript, in turn, downloaded the payload that would be either Locky or Trickybot.

But that apart, the downloader also executed a PowerShell script that made a screenshot and saved it as generalpd.jpg. After this was saved, it was uploaded to a remote server.

"Much like crash reports in OSes can help software companies fix issues and build better products, these error reports can help attackers spot problems in the field and address them to improve success rates. After all, you can’t count on the victims to report back errors and issues!" researchers Eduardo Altares, Wei Wang Dai, and Mingwei Zhang wrote.

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Symantec telemetry shows Necurs emails with script attachments have grown fourfold since June.

The researchers said the best way to avoid getting caught by one of these emails was to:

  • Delete any suspicious-looking emails you receive, especially if they contain links or attachments;
  • Always keep your security software up-to-date to protect yourself against any new variants of malware;
  • Keep your operating system and other software updated. Software updates will frequently include patches for newly discovered security vulnerabilities that could be exploited by attackers; and
  • Regularly back up any files stored on your computer. If your computer does become infected with ransomware, your files can be restored once the malware has been removed.

Cover graphic: courtesy Microsoft. Article-level graphics: courtesy Symantec

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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.