Malware

Dofoil Trojan used to deploy cryptocurrency miner on more than 500,000 PCs in a few hours

Microsoft experts observed more than more than 500,000 computers infected with Dofoil Trojan used to download a cryptocurrency miner.

A few days ago, researchers at Microsoft announced that Windows Defender Antivirus blocked more than 80,000 instances of several malicious code that exhibited advanced cross-process injection techniques, persistence mechanisms, and evasion methods.

According to Microsoft, the malware were new variants of Dofoil (also known as Smoke Loader), a small application used to download other malicious codes, in these specific attacks a coin miner. The cryptocurrency miner payload was used to mine Electroneum coins.

In Just 12 hours from the discovery, the experts observed more than 400,000 instances, most of them in Russia (73%), Turkey (18%) and Ukraine (4%).
Totally more than 500,000 computers were infected within just 12 hours.

The Dofoil trojan uses an old code injection technique called ‘process hollowing’ that was recently observed by researchers at CSE CybSec implemented in evolutive versions by another malware.

“The trojans, which are new variants of Dofoil (also known as Smoke Loader), carry a coin miner payload. Within the next 12 hours, more than 400,000 instances were recorded, 73% of which were in Russia. Turkey accounted for 18% and Ukraine 4% of the global encounters.” reads the analysis published by Microsoft.

“The Dofoil campaign we detected on March 6 started with a trojan that performs process hollowing on explorer.exe. Process hollowing is a code injection technique that involves spawning a new instance of legitimate process (in this case c:\windows\syswow64\explorer.exe) and then replacing the legitimate code with malware.”

The analysis of the Dofoil malware revealed it uses a customized mining application that supports NiceHash allowing infected systems to mine different cryptocurrencies even if the samples Microsoft analyzed mined Electroneum coins.

The malware gain persistence on an infected system through the Windows registry, hollowed explorer.exe process creates a copy of the original malware in the Roaming AppData folder and renames it to ditereah.exe. The malicious code then creates/modifies a registry key to modify an existing one to point to the newly created malware copy.

Threat actors behind the Dofoil campaign used a command and control (C&C) server hosted on decentralized Namecoin network infrastructure.

“The C&C server commands the malware to connect or disconnect to an IP address; download a file from a certain URL and execute or terminate the specific file; or sleep for a period of time.” states Microsoft.

Microsoft confirmed that its Windows Defender Antivirus is a crucial component for detecting and blocking advanced threats.

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Pierluigi Paganini

(Security Affairs – Dofoil, cryptocurrency miner)

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Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.

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