Fileless Malware: A Comprehensive Guide In 2021

Ajay Ohri


Cybersecurity counter-measures are evolving so is the malware industry with the release of sophisticated malware that is more effective than the traditional executable files. Fileless malware, as the name suggests, does not require files to carry out its malicious activities. Rather, it uses built-in Microsoft tools and applications to launch its attacks against the operating system. Fileless attack causes innumerable damages to business houses and corporates at a greater scale.

It does not leave any footprints as it is more persistent and challenging to detect even with some of the most sophisticated security software. It has the capacity to reside in the computer’s main memory for a long time without getting detected and exploits the legitimate Windows applications to work against its own system. 

  1. Definition
  2. Why Hackers Choose Fileless Malware?
  3. How Fileless Malware Work?
  4. How to Detect Fileless Malware?
  5. Types of Fileless Malware

1. Definition 

What Is Fileless Malware? Cybercriminals and hackers try and find ways to install malicious software programs on the target computers. The security software is designed in such a way that it detects such attempts and looks for malicious programs as the system is compromised. However, in the case of Fileless Malware, there are no malicious files as it does not reside in the file system rather it dwells in the system memory. Therefore, it remains undetected by the security software and remains a security challenge as it is memory-based and not file-based. 

2. Why Hackers Choose Fileless Malware?

Fileless malware attacks have become so common nowadays. The 2017 Equifax fileless attack was one of the largest data breaches that rocked the Cybersecurity world. Studies have also estimated that more than 70% of all breaches are fileless attacks and are more likely to be successful than other file-based attacks. There are some underlying reasons as to why cyber attackers and hackers prefer files malware over file-based attacks. They are:

  • The security software is unable to detect the fileless malware effectively as they can reside in the system for a longer period of time.
  • It allows them to gain administrative access and thus allowing them to leverage the existing applications to perform their malicious activities.
  • It makes the target computer vulnerable for future attacks and lays down the groundwork for it.

3. How Fileless Malware Work?

Unlike traditional malware, Fileless Malware checks for vulnerable software applications in the target computer to carry out its attack. They take control of this software to infect and carry out the attack. Moreover, they do not need to be downloaded as malicious files or software to infect a system. They rather use the system services of the target computer to get access and carry out their malicious activities without getting detected. For instance, they use trusted utilities like Windows Management Instrumentation (WMI) and Windows Powershell to execute malicious activities. Thus, they remain undetected for a long time as these are legitimate software. 

Security software finds it difficult to detect this fileless malware as there are no stored files associated with it. Moreover, it leaves no footprint or any sort of pieces of evidence to identify that a breach took place in actuality. However, as these files are stored in the computer’s main memory, the intruder is left with no choice but to reinitiate the attack if the system is rebooted. 

Hackers launch their attacks as internet users click on links provided in phishing emails and other website links. The objective of such attacks is to gain access to various systems across the company’s network using trusted software applications. As security software are designed to limit the monitoring of trusted and legitimate software applications, this fileless malware takes leverage and exploit this opportunity. 

4. How to Detect Fileless Malware?

It is not practical to reboot the system repeatedly over a period of time just to make sure fileless malware is not transferred into the system or the computer network. One best way to tackle this malicious activity is to keep the system software updated from time to time. Although these malware attacks are difficult to detect as they leave no traces or footprints, they can be prevented by monitoring network patterns and analyzing applications that are liable to get infected.

Fileless Malware detection requires a holistic and integrated approach. Some of the best practices that users need to follow at the individual levels are –

  • Users need to keep the applications and security software updated.
  • Users need to have a watchful eye while downloading files from websites.
  • Besides updating the system software, users need to update web browsers as well.
  • While checking emails, users need to look out for phishing emails that may contain unscrupulous links.
  • Rebooting the system once in a while can help stop the malware breach.
  • Uninstalling or turning off unnecessary software applications and features or add-ons may help as well.

5. Types of Fileless Malware

There are many types of Fileless Malware, but it can be categorized under three primary heads –

  • Windows Registry Manipulation – The fileless malware uses malicious links and files to target the system registry by editing and executing codes into the registry.
  • Memory Code Injection – It uses the memory of legitimate system applications and infects the system processes that are critical in running the Windows operating system.
  • Script-based Infection – These are very hard to detect and are semi-fileless. It requires the hacker’s credentials to make changes and is constantly evolving. These attacks are mainly aimed at targeted systems and are single-purpose in nature. SamSam is one such fileless ransomware. 


Organizations need to ramp up security infrastructure and software tools to detect and prevent malware attacks. Any security breaches need to be examined and validated for further action by the security analyst. He needs to stay ahead of the intruders by keeping up with the latest developments in countering this menace. They should stay the course and remain focus on detecting and preventing malware attacks.

Security professionals need to constantly upgrade their knowledge and evolve from traditional methods to counter malware attacks. Only then organizations can secure an environment void of fileless malware and other advanced cyber-attacks. Thus, cyber threats have evolved so are the countermeasures in securing organizations through pre-emptive research and analysis.

So, have you made up your mind to make a career in Cyber Security? Visit our Master Certificate in Cyber Security (Red Team) for further help. It is the first program in offensive technologies in India and allows learners to practice in a real-time simulated ecosystem, that will give you an edge in this competitive world.

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