Fileless Malware


Fileless malware is a type of malicious software that operates without writing any files to the victim’s computer system. Instead, it utilizes legitimate system tools and processes, such as PowerShell or Windows Management Instrumentation, to execute its payload directly in memory. This stealthy approach makes fileless malware more challenging to detect and remove, as it leaves minimal traces behind for traditional antivirus software to identify.


Fileless Malware in phonetics is: /ˈfaɪl.lɪs ˈmæl.wer/

Key Takeaways

  1. Fileless malware operates by running directly in system memory or leveraging legitimate system tools to execute malicious code, making them difficult to detect with traditional antivirus solutions.
  2. Fileless malware attacks can be highly sophisticated, involving multiple stages such as infiltration, persistence, and extraction of sensitive information, often using popular scripting languages like PowerShell or JavaScript.
  3. Preventing fileless malware requires a strong focus on system, network, and user behavior monitoring, as well as implementing good security practices, including regular software updates and employee cybersecurity training.


Fileless malware is important because it represents a significant evolution in cyber threats, posing a greater challenge for cybersecurity professionals and organizations to detect, prevent, and remediate infections.

Unlike traditional malware that relies on files to execute and spread, fileless malware exists exclusively in-memory and leverages legitimate tools and applications already installed on a target system to carry out malicious activities.

This stealthy approach enables it to evade traditional antivirus and security solutions, making it more difficult to trace and mitigate.

Consequently, understanding and addressing fileless malware is critical to ensure the safety of both businesses and individuals in the digital landscape.


Fileless malware represents a unique breed of cyberthreat, designed to carry out high-level intrusions without leaving a detectable footprint on the target system. The primary purpose of its development is to avoid traditional anti-malware defenses while causing damage, theft of sensitive information, or even gaining control of the target system. Conventional malware relies on executable files and other on-disk traces, which make them easier to detect and neutralize.

However, fileless malware cunningly uses system memory, scripts, and other in-built tools to bypass these protections, which makes it a formidable weapon in the hands of cybercriminals. One of the primary reasons behind the increasing adoption of fileless malware by cybercriminals is its versatility in achieving its nefarious goals. By using legitimate system resources, this type of malware can exploit various system vulnerabilities, subsequently launching devastating attacks.

For example, adversaries can execute fileless attacks through PowerShell scripts, Microsoft Office macros, or by leveraging Windows Management Instrumentation (WMI) services. Since the malware remains concealed within seemingly legitimate processes, it becomes extremely challenging for traditional security systems to detect and mitigate the threat promptly. Consequently, fileless malware continues to be an evolving challenge for businesses and security experts in their ongoing efforts to safeguard data and digital infrastructure against advanced and persistent threats.

Examples of Fileless Malware

Fileless malware is a type of cyberattack that does not rely on traditional executable files to infiltrate a system and carry out malicious activities. Instead, it leverages trusted system tools, scripts, or applications already installed on a victim’s computer. Here are three real-world examples of fileless malware:

PowerWare (also known as PoshCoder):PowerWare is a type of ransomware that utilizes the built-in Windows PowerShell scripting tool to infect a victim’s system. First discovered in 2016, it targeted victims via phishing emails with malicious macros embedded in Microsoft Word documents. Once downloaded and executed, PowerWare used PowerShell to encrypt the user’s files and demand a ransom for decrypting the data.

Kovter:Kovter is a click-fraud malware that relies on JavaScript, batch files, and shortcuts for execution and persistence on the victim’s machine. Initially discovered in 2011, it has evolved over time to include fileless capabilities. By utilizing the Windows Registry to store its payloads and additional commands, Kovter bypasses traditional security solutions that look for malicious files and achieves persistence on the infected system.

Astaroth (also known as Guildma):Astaroth is a fileless Trojan that was discovered in 2018, primarily targeting users in Brazil. It leverages the Windows Management Instrumentation Command-line (WMIC) tool and JavaScript to download and execute payloads directly from command scripts. The malware infiltrates a system through phishing emails with malicious links and uses a multi-stage attack strategy, living off the land to avoid detection. Astaroth is involved in an array of malicious activities, such as collecting sensitive information, keystroke logging, and credential stealing.

FAQ: Fileless Malware

What is fileless malware?

Fileless malware is a type of malicious software that operates without writing any files on the disk. It resides in the computer’s memory or leverages legitimate system tools to propagate and execute its malicious activities, making it difficult for traditional antivirus tools to detect and remove.

How does fileless malware infect a system?

Fileless malware often infects a system through phishing emails, malicious websites, or by exploiting software vulnerabilities. Once on the system, it leverages legitimate tools like PowerShell, Windows Management Instrumentation (WMI), or other scripting languages to perform its activities, leaving no trace on disk.

What makes fileless malware particularly dangerous?

Fileless malware is considered dangerous because it is difficult to detect and remove due to its lack of presence on disk. It avoids detection by traditional antivirus tools, and because it leverages legitimate tools for malicious purposes, it can easily blend in with normal system activities. Moreover, fileless malware can easily spread and infect other systems on the network.

How can I protect my system from fileless malware?

Protecting your system from fileless malware involves a combination of strategies, such as keeping your operating system and software up-to-date, using a robust antivirus solution with behavioral monitoring, avoiding suspicious emails and websites, and employing strict user access controls. Additionally, disabling scripting tools like PowerShell on systems where they are not needed can also provide extra protection.

How can fileless malware be detected and removed?

Since fileless malware is difficult to detect using traditional antivirus tools, advanced security solutions that use behavioral analysis and artificial intelligence are recommended for detecting and removing fileless malware. Regular monitoring of logs and network traffic can also help identify suspicious activities. In case of infection, a system reboot may help remove malware from memory, but additional steps may be needed to ensure complete removal and prevent reinfection.

Related Technology Terms

  • Lateral Movement
  • PowerShell
  • Memory Injection
  • Non-malware attack
  • Living off the Land (LOL)

Sources for More Information


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