What is Fileless Malware? Everything You Need to Know (2023)

By Tibor Moes / Updated: June 2023

What is Fileless Malware? Everything You Need to Know (2023)

What is Fileless Malware?

As technology advances and our reliance on digital systems increases, so too does the sophistication and persistence of cyber threats. One such evolving menace is fileless malware, a formidable adversary that operates on a whole new level of stealth and cunning. But what is fileless malware exactly, and what makes it so elusive and dangerous?

In this blog post, we’ll delve into the world of fileless malware, exploring its defining characteristics, methods of infiltration, common techniques, and notable attacks. We’ll also discuss strategies for detection and prevention, empowering you with the knowledge needed to defend against this insidious threat.


  • Fileless malware is a type of malicious software that operates in a computer’s memory rather than installing itself on the hard drive.

  • It uses legitimate system tools and services to perform malicious activities, making detection and removal difficult.

  • Regular system updates, limited user permissions, and behavior-based detection tools can help protect against fileless malware.

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Defining Fileless Malware

Fileless malware is a type of malicious code that runs in memory and doesn’t need any files stored on disk. This memory-based nature allows it to hide within legitimate applications and exploit existing vulnerabilities in browsers and programs like Java and Flash, as well as infiltrate systems through phishing campaigns. The result? A highly stealthy form of malware that can remain undetected by traditional antivirus software and endpoint security products.

Detecting fileless malware is no easy feat, and neither is preventing it. To counter this threat, organizations must adopt a multi-layered approach that encompasses system updates and patching, employee cybersecurity training, and monitoring native tools. By understanding the intricacies of fileless malware and staying vigilant in our defenses, we can minimize the risks posed by this elusive cyber adversary.

How Fileless Malware Infiltrates Systems

Fileless malware primarily gains access to computer systems by exploiting system vulnerabilities or through phishing campaigns.

In the following subsections, we’ll explore these two methods in more detail, shedding light on how fileless malware can infiltrate systems and execute its malicious activities.

Exploiting Software Vulnerabilities

Software vulnerabilities are defects or weaknesses in software that can be used by attackers to gain access to systems or carry out malicious activities. Fileless malware can exploit these weaknesses in commonly used software and applications, allowing it to gain access to the system and execute malicious code without needing to download a file. Some infamous examples of fileless malware exploiting software vulnerabilities include WannaCry ransomware, which targeted a vulnerability in the Windows OS, and NotPetya malware, which exploited a vulnerability in the Windows Server Message Block protocol.

To prevent fileless malware from taking advantage of software vulnerabilities, it’s crucial to keep systems updated and patched, provide employees with cybersecurity training, and closely monitor native tools. By staying vigilant and proactive, we can minimize the chances of falling victim to fileless malware attacks.

Phishing Campaigns

Phishing is a type of social engineering attack that involves sending malicious emails or links to unsuspecting victims. Attackers use these emails to try and get victims to click malicious links or download malicious attachments, which can then be used to deliver fileless malware payloads. Microsoft Office and PDF readers are particularly vulnerable, providing ample opportunities for attackers to run malicious code.

One notable example of a fileless malware attack that leveraged phishing campaigns is Operation Cobalt Kitty, where a spear-phishing email was used to compromise over 40 PCs and servers within an Asian corporation.

By educating employees on how to recognize and avoid phishing attempts and social engineering tactics, organizations can reduce the likelihood of fileless malware infiltrating their systems through such campaigns.

Common Fileless Malware Techniques

Fileless malware employs a variety of stealthy techniques to bypass detection and wreak havoc on its victims. Some of the most common strategies include memory code injection, Windows registry manipulation, and leveraging native tools.

In the following subsections, we’ll delve deeper into each of these techniques, illustrating their cunning nature and capacity to evade traditional security measures.

Memory Code Injection

Memory code injection is a technique that allows fileless malware to hide malicious code within the memory of legitimate applications, enabling it to execute without being detected. By exploiting vulnerabilities in commonly targeted programs like Flash, Java, and browsers, fileless malware can inject its malicious code into the target computer’s memory and remain virtually invisible to traditional antivirus software.

To further aid in evading detection, fileless malware often utilizes packers – tools that compress the malware files while still allowing them to carry out their code and function. This combination of memory code injection and packers enables fileless malware to operate undetected, posing a significant challenge for security professionals and organizations alike.

Windows Registry Manipulation

Windows Registry Manipulation is another technique employed by fileless malware, using the Windows Registry database to store and run malicious code. When a malicious file or link is clicked on, the normal Windows process is utilized by the malware. It writes and executes fileless code into the registry. This makes it extremely difficult for antivirus software to detect and remove malicious code, as it is embedded within a legitimate Windows process.

By manipulating the Windows registry in this manner, fileless malware can maintain persistence on the infected system and continue to carry out its malicious activities. Organizations must remain vigilant in monitoring their systems for unusual activity and potential registry manipulations in order to effectively detect and combat this stealthy threat.

Leveraging Native Tools

Fileless malware is also known to exploit built-in system tools like PowerShell and Windows Management Instrumentation (WMI) to execute malicious activities. These native tools are often trusted by security solutions and are typically overlooked during routine security scans, making them an ideal vehicle for fileless malware to carry out its covert operations.

By exploiting native tools in this manner, fileless malware can maintain a low profile and avoid detection by traditional security measures. Organizations must be vigilant in monitoring the use of native tools within their systems and be prepared to investigate any unusual activity or behavior that may indicate the presence of fileless malware.

Notable Fileless Malware Attacks

Fileless malware has been responsible for several high-profile attacks, demonstrating its impact and sophistication. Some notable examples include the hack of the Democratic National Committee, the Equifax breach, and the SQL Slammer worm. Other infamous fileless malware strains include Kovter, USB Thief, PowerSniff, and Poweliks.

Additionally, script-based attacks like SamSam ransomware and Operation Cobalt Kitty have also made headlines, showcasing the adaptability and potency of fileless malware techniques. These incidents serve as a stark reminder of the growing threat posed by fileless malware and the need for organizations to remain vigilant in their cybersecurity efforts.

Detecting Fileless Malware

Detecting fileless malware is a significant challenge, as traditional detection methods based on signatures, rules, and scans are often ineffective against these stealthy threats. However, alternative approaches such as monitoring Indicators of Attack (IOAs) and employing managed threat hunting services can help organizations identify and mitigate fileless malware threats.

In the following subsections, we’ll explore these detection strategies in more detail.

Indicators of Attack (IOAs)

Indicators of Attack (IOAs) are unusual behaviors that could signal the presence of fileless malware within a system. By monitoring IOAs, organizations can not only identify fileless malware, but also prevent it from spreading or carrying out the attack sequence. Continuous, real-time monitoring is critical for detecting any abnormal activity related to fileless malware, allowing security teams to respond swiftly and effectively to potential threats.

Behavioral analysis, a key component of IOA monitoring, can spot abnormal and suspicious activities that might otherwise go unnoticed by traditional detection technologies. By focusing on the behavior of processes and applications within their systems, organizations can better detect and protect against fileless malware attacks.

Managed Threat Hunting

Managed threat hunting is a service provided by experienced cybersecurity companies that actively search for and mitigate fileless malware threats. These services go beyond traditional security technologies and employ advanced techniques, such as machine learning-based behavioral analytics, to detect and respond to subtle activities that may indicate the presence of fileless malware.

By leveraging managed threat hunting services, organizations can benefit from the expertise and experience of dedicated security professionals who are well-versed in the latest fileless malware threats and techniques. This proactive approach to threat detection and mitigation can greatly enhance an organization’s overall cybersecurity posture and help keep fileless malware at bay.

Preventing Fileless Malware Attacks

To effectively protect against fileless malware threats, organizations must adopt an integrated approach that combines multiple security measures, such as regular system updates and patching, employee cybersecurity training, and monitoring native tools.

In the following subsections, we’ll explore these prevention strategies in more detail, providing guidance on how to build a robust defense against fileless malware attacks.

Regular System Updates and Patching

Keeping software and operating systems up-to-date and patched is a critical component of any cybersecurity strategy. Regular system updates and patching involve updating and fixing any vulnerabilities in software and operating systems to ensure that the system is secure and protected against potential threats, such as fileless malware attacks.

By staying current with the latest software updates and patches, organizations can minimize the risk of fileless malware exploiting known vulnerabilities in their systems. This proactive approach to system maintenance can greatly reduce the likelihood of falling victim to fileless malware attacks and help maintain a secure computing environment.

Employee Cybersecurity Training

Implementing cybersecurity awareness training for employees is another essential measure in defending against fileless malware attacks. This training should cover topics such as password management, phishing awareness, and safe browsing practices, empowering employees with the knowledge and skills needed to recognize and avoid phishing attempts and social engineering tactics that may be used to deliver fileless malware payloads.

By investing in employee cybersecurity training, organizations can strengthen the human element of their security strategy and reduce the risk of employees inadvertently enabling fileless malware attacks through careless or uninformed actions.

Monitoring Native Tools

Closely monitoring native operating system tools is another crucial aspect of defending against fileless malware attacks. Fileless malware often exploits trusted native tools like PowerShell and Windows Management Instrumentation (WMI) to carry out malicious activities without leaving a trace on the system. By keeping a close eye on the usage of these native tools, organizations can detect unusual activity that may indicate the presence of fileless malware.

Monitoring native tools can be achieved by leveraging the built-in monitoring tools provided by the operating system or cloud platform, allowing organizations to track the performance and behavior of applications and infrastructure, as well as detect any suspicious activities, such as unexpected processes, network connections, or file access.

By remaining vigilant and proactive in monitoring native tools, organizations can effectively detect and combat fileless malware threats.


In today’s rapidly evolving threat landscape, fileless malware has emerged as a formidable adversary that poses significant challenges to organizations and individuals alike. Its memory-based nature and ability to exploit existing vulnerabilities and native tools make it a stealthy and dangerous foe. As we’ve explored in this blog post, detecting and preventing fileless malware attacks requires an integrated approach that combines regular system updates and patching, employee cybersecurity training, and vigilant monitoring of native tools.

In the face of this growing threat, it is more important than ever for organizations to remain proactive and vigilant in their cybersecurity efforts. By understanding the intricacies of fileless malware and implementing robust security measures, we can minimize the risks posed by this insidious cyber adversary and continue to operate in a secure and resilient digital environment.

How to stay safe online:

  • Practice Strong Password Hygiene: Use a unique and complex password for each account. A password manager can help generate and store them. In addition, enable two-factor authentication (2FA) whenever available.
  • Invest in Your Safety: Buying the best antivirus for Windows 11 is key for your online security. A high-quality antivirus like Norton, McAfee, or Bitdefender will safeguard your PC from various online threats, including malware, ransomware, and spyware.
  • Be Wary of Phishing Attempts: Be cautious when receiving suspicious communications that ask for personal information. Legitimate businesses will never ask for sensitive details via email or text. Before clicking on any links, ensure the sender's authenticity.
  • Stay Informed. We cover a wide range of cybersecurity topics on our blog. And there are several credible sources offering threat reports and recommendations, such as NIST, CISA, FBI, ENISA, Symantec, Verizon, Cisco, Crowdstrike, and many more.

Happy surfing!

Frequently Asked Questions

Below are the most frequently asked questions.

What does fileless malware do?

Fileless malware is a type of cyberattack that exploits existing applications, utilities, and legitimate processes to gain access to a system or network. It’s particularly difficult to detect because no malicious code is stored on the targeted device. As a result, it can be difficult to detect and protect against this type of attack.

Traditional security solutions, such as antivirus software, are not designed to detect fileless malware. Organizations must take proactive steps to protect their systems and networks from this type of attack. This includes implementing security measures such as application whilet.

What is an example of fileless malware?

Fileless malware is a type of attack that does not rely on the use of a file to run malicious code in the background. Examples of this include tactics such as PowerShell scripts, using legitimate programs for malicious purposes, and WMI (Windows Management Instrumentation).

These attacks are becoming increasingly popular due to their ability to bypass traditional security measures. They are difficult to detect and can be used to gain access to sensitive data or systems. Additionally, they can be used to launch other products.

What is the difference between file and fileless malware?

The key difference between fileless malware and traditional malware is that the former runs in the computer’s memory without any files being written to the disk. Fileless malware often uses legitimate, built-in applications or system tools to carry out malicious operations, making it more difficult to detect.

What is fileless malware email?

Fileless malware is a form of malicious attack that does not require any files to be downloaded, and instead uses existing applications in a computer’s memory to carry out its mission. This makes it difficult to detect and can easily pass through antivirus software, making it a more dangerous form of malware for businesses and individuals alike.

Author: Tibor Moes

Author: Tibor Moes

Founder & Chief Editor at SoftwareLab

Tibor is a Dutch engineer and entrepreneur. He has tested security software since 2014.

Over the years, he has tested most of the best antivirus software for Windows, Mac, Android, and iOS, as well as many VPN providers.

He uses Norton to protect his devices, CyberGhost for his privacy, and Dashlane for his passwords.

This website is hosted on a Digital Ocean server via Cloudways and is built with DIVI on WordPress.

You can find him on LinkedIn or contact him here.

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