Necurs

Category: Malware

Type: Botnet/Downloader/Spambot

Platform: Windows

Variants: Multiple evolving versions with rootkit and spam capabilities

Damage potential: Distributes various malware, including ransomware and banking trojans, which causes significant financial losses worldwide.

Overview

Necurs is a powerful botnet primarily targeting Windows systems. It spreads through email spam campaigns and delivers malicious attachments, such as ransomware or banking trojans. Once a system is infected, Necurs acts as a downloader and installs additional malware.

The botnet turns compromised machines into part of a massive network, which cybercriminals can control remotely. Necurs uses a hybrid command-and-control system, which makes it highly resistant to takedown efforts.

Necurs has caused significant financial damage in various cyberattacks. This malware is attributed to the threat actor group Monty Spider, known for its involvement in large-scale cybercrime operations. Discovered in 2012, Necurs was disrupted in 2020 through a coordinated effort by Microsoft, law enforcement, and cybersecurity firms. However, even though Necurs itself is largely inactive, remnants of its infrastructure or techniques may still be seen in other malware campaigns or botnets.

Possible symptoms

Necurs infections can significantly affect system performance and security by turning infected machines into part of a botnet and distributing malicious payloads. Symptoms of a Necurs infection include:

• Sluggish or unresponsive system performance.
• Unusual network activity or unexpected outbound connections to suspicious IP addresses.

• Increased CPU or memory usage.
• Unknown or suspicious processes running on the system, often with names that mimic legitimate services.
• Presence of hidden files or libraries loaded via user-mode rootkits, making it difficult to detect the malware.
• Presence of email spam processes or outbound mail traffic.
• Unexplained system instability or crashes.

Sources of the infection

Cybercriminals use multiple methods to spread the Necurs botnet and install its malicious payloads:

• Email spam campaigns. Necurs primarily spreads through large-scale email campaigns, where cybercriminals make the emails appear as legitimate communications to trick users into opening malicious attachments or clicking on links.
• Exploitation of software vulnerabilities. Necurs can exploit vulnerabilities in outdated or unpatched software to gain access to target systems, bypass security measures, and install itself on vulnerable machines.
• Social engineering tactics. Cybercriminals use phishing emails or fake software updates to trick users into downloading and executing Necurs by mimicking legitimate communication from trusted organizations.
• Lateral movement within networks. Once a system is infected, Necurs can scan the network for other vulnerable machines and spread laterally.
• Drive-by downloads. Necurs can also spread through compromised or malicious websites that automatically download and install the malware on your machine when you visit the site.

Protection

The best way to protect against Necurs is by securing systems and networks against the methods it uses to spread. Measures to protect against Necurs include:

• Using antivirus and anti-malware software. Install and regularly update reliable security solutions that can detect and block Necurs, as well as other malware that it may distribute, such as ransomware and banking trojans.
• Regularly updating systems and software. Keep your operating system, email clients, and all applications up to date to patch vulnerabilities that Necurs may exploit, such as outdated software or unpatched security holes.
• Improving email security. Apply email filtering solutions that detect and block spam and phishing emails, and educate users on the risks of opening suspicious attachments or clicking on untrusted links.
• Configuring firewalls and intrusion detection systems (IDS). Set up firewalls and IDS to block unusual network activity, such as unexpected outbound connections to command-and-control servers that Necurs may initiate.
• Restricting access to sensitive ports. Limit access to critical services such as email servers and ensure they are not exposed to the internet without proper authentication and secure configurations.
• Disabling unnecessary services. Turn off any unused or unnecessary services that could serve as entry points for Necurs, such as open email ports or remote desktop access.
• Implementing multi-factor authentication (MFA). Use MFA for email and critical administrative accounts to prevent unauthorized access, even if credentials are compromised.
• Monitoring system and network activity. Regularly monitor network traffic, system performance, and email activity for unusual behavior, such as unexplained spikes in CPU or memory usage.

Removal of Necurs

If you suspect your system is infected with Necurs, follow these steps to remove it:

1. 1.Isolate the device. The first thing you’ll want to do is disconnect the infected machine from your network to stop the malware from spreading.
2. 2.Scan and clean. Use a trusted antivirus or anti-malware program to run a full system scan. These tools are designed to find and remove malware and its hidden components.
3. 3.Update and secure. Once the threat is gone, update all your software with the latest security patches. This helps close the vulnerabilities that Necurs may have used to get in.
4. 4.Call for backup. If you’re still having trouble removing Necurs, you should reach out to a cybersecurity expert for help.