Rootkits that put the hacker in control

What are rootkits?

A rootkit is a type of malicious software that gives unauthorized users administrative-level access to a system. The term rootkit in cybersecurity refers to a set of malicious software tools that enable threat actors to remotely access, control, and manipulate a device, often while evading detection. The word “rootkit” comes from “root,” meaning administrator, and “kit,” meaning a set of tools. In essence, a rootkit is a toolkit that grants full control over a device.

Because rootkits provide such elevated access, they pose a serious risk to any system they infect. Rootkits are often used for malicious purposes, such as to gain unauthorized access and root level access to systems, allowing attackers to steal data, maintain control, or install additional malware. Hackers can use them to monitor activity, steal sensitive information, disable security programs, or install additional malware. Unlike many other forms of malware, rootkits are designed to stay hidden. They often go undetected by antivirus software and can operate in secret for long periods of time.

Why are rootkits so dangerous?

Rootkits are not just another form of malware – they are among the most sophisticated and persistent threats in cybersecurity. What makes them especially dangerous is their ability to operate silently while giving attackers deep access to a system. Once a rootkit is installed, it can evade detection, disable security measures, and allow hackers to carry out long-term attacks without the user’s knowledge. Below, we explore the key reasons rootkits pose such a serious risk.

Stealth and invisibility

Rootkits are built to be invisible. Once installed, they can operate remotely, monitoring and controlling a system without leaving visible traces. They are typically delivered through phishing emails, where cybercriminals trick users into downloading malicious files – such as infected executables, PDFs, or Word documents – that may contain rootkits.

Security bypass

Rootkits can disable security software to evade detection, override security tools, change system settings, and block antivirus software. This makes detection and removal extremely difficult.

Privileged access

With administrative-level privileges, hackers gain access to the core of a system. This is especially dangerous when IT administrators are compromised, since they have broader access than regular employees. With this level of access, hackers can also steal sensitive data from the system.

Subtle symptoms

Rootkits do not usually cause pop-ups or noticeable errors. Instead, they run silently in the background. This lack of symptoms allows them to bypass even the most advanced security systems.

What can rootkits do?

Rootkits are highly versatile and can:

• Record keystrokes and log keystrokes

• Steal login credentials and sensitive data

• Disable antivirus and firewall protections

• Monitor user activity

• Install and launch additional malware, including other malware

• Infect computers to install malware directly onto a device's firmware

• Create remote backdoors

Advanced rootkits may even allow hackers to deploy bots and turn an infected computer or infected machine into part of a larger botnet, often in combination with other malware.

If you're unsure what malware is or want to understand it better, read our guide on what malware is. You can also learn more about botnets and how they are used in cyberattacks in our article on what a botnet is and how it is used.

Types of rootkits

Rootkits are categorized by how they infect and persist on different operating systems and the specific target system. Different rootkits serve different purposes. Here are the most common types:

Firmware rootkit

Firmware rootkits target the software installed on a device's firmware, such as the BIOS or UEFI. Because firmware operates below the operating system, these rootkits are extremely difficult to detect or remove.

Firmware rootkits can also pose a significant threat to virtual machines running on shared hardware, as compromising the underlying firmware can impact all virtualized environments on the same physical system.

Memory rootkit

This type of rootkit hides in the RAM, or temporary memory, of a computer. It typically disappears after a reboot but can slow down the system while active.

Memory dump analysis is often used to detect memory rootkits by examining a system's memory for hidden malicious instructions.

Kernel rootkit

Kernel rootkits, also known as kernel mode rootkit, attack the core of the operating system. Unlike user mode rootkits, which operate in user mode and manipulate application programming interfaces (APIs) to alter application behavior and hide their presence, kernel rootkits operate at the kernel level, giving hackers full control over essential system processes and making them among the most dangerous types of rootkits.

Bootloader rootkit

Bootloader rootkits often target the master boot record, infecting the system before the operating system starts. They take control during startup, making them difficult to detect. Secure boot is a security feature designed to prevent unauthorized or malicious bootloaders from executing before the operating system starts. However, most modern devices include built-in protections against these rootkits.

Application rootkit

Application rootkits may replace or modify standard applications, resulting in infected programs that allow unauthorized access while remaining hidden from typical detection methods. Every time the user opens the program, the hacker gains insight into their activity. These rootkits are easier to detect because they often cause programs to behave strangely.

Rootkit techniques and tactics

Rootkits use advanced techniques to stay hidden and maintain control:

• Kernel mode manipulation: Altering the operating system’s kernel to execute commands with the highest level of authority.

• Code injection: Injecting malicious code into legitimate system processes to hide activity.

• API hooking: Intercepting and modifying system calls to manipulate how programs interact with the operating system.

• Intercepting hardware calls: Some advanced rootkits can intercept hardware calls by operating beneath the host OS, allowing them to manipulate device interactions without altering the kernel.

• File system manipulation: Modifying or hiding files to avoid detection by file management tools.

• Network traffic manipulation: Intercepting and changing network traffic to steal data or communicate with external servers.

Behavioral analysis can detect rootkit like behaviors by identifying suspicious patterns and activities that indicate a rootkit infection, even before traditional detection methods find the threat.

Symptoms of rootkit infection

Although rootkits aim to stay invisible, there are warning signs to watch for:

• Unexpected system crashes or freezes

• Slower performance than usual

• Security programs that fail to open or update

• Unusual network activity or data transfers

• System settings that change without your input

• Unexpected changes to Windows settings, such as screensaver, taskbar, or date/time configurations.

If several of these symptoms occur, your system may be infected with a rootkit, as these are common signs of rootkit infections.

Real-world rootkit attacks

Several high-profile cyberattacks have involved rootkits. These attacks often begin with rootkit installation, exploiting system vulnerabilities or infected USB drives to secretly deploy malicious software. Because rootkits are difficult to detect and remove, robust rootkit protection is essential to safeguard systems against such threats.

• Stuxnet: Targeted Iranian nuclear facilities by damaging centrifuges. Stuxnet showed how rootkits can cause real-world physical damage.

• Duqu: Used in cyber espionage campaigns to gather intelligence, particularly in the Middle East.

• Flame: Collected sensitive data including screenshots, audio, and keystrokes. It is considered one of the most advanced rootkits ever developed.

• ZeroAccess: Infected millions of computers worldwide. Used for creating botnets and conducting large-scale fraud operations.

• Spicy Hot Pot: Linked to Chinese state-sponsored actors who used rootkits for long-term cyber espionage and data theft.

Detecting and preventing rootkits

Detection

Rootkits can be difficult to detect with standard tools, but certain signs may indicate an infection:

• Frequent software or system failures

• Inability to launch antivirus software

• Presence of unknown programs or files

In some cases, specialized tools or boot-level scans are necessary to identify a rootkit. Detecting rootkits often involves running dedicated rootkit scans that use advanced rootkit detection techniques, such as memory dump analysis and behavioral analysis, to uncover hidden or stealthy malware infections. In severe cases, the safest solution is to format the hard drive and reinstall the operating system.

Prevention

To reduce your risk of infection, follow these best practices:

• Run regular malware scans: Scanning your systems regularly helps identify and remove hidden threats.

• Stay alert to phishing attempts: Avoid clicking links or downloading attachments from unknown sources. Phishing remains one of the most common delivery methods for rootkits.

• Train your team in cybersecurity: Awareness training helps employees recognize suspicious emails and links.

• Keep software up to date: Regularly update your software to fix security flaws that could otherwise be exploited by rootkits.

• Enable security features for rootkit protection: Turn on security features such as Secure Boot and built-in OS protections to help prevent rootkit infections and improve rootkit protection.

Removing rootkits

Eliminating rootkits from a compromised system is often far more complex than removing other types of malicious software. Because rootkit malware is designed to hide deep within a computer’s core components, standard removal methods may not be effective – especially when dealing with advanced kernel mode rootkits, bootloader rootkits, or firmware rootkits.

The first step in rootkit removal is identifying the specific type of rootkit infecting your system. Kernel mode rootkits, for example, embed themselves in the operating system’s kernel, making them extremely difficult to detect and remove without specialized tools. Bootloader rootkits compromise the boot process, taking control before the operating system even starts, while firmware rootkits infect the device’s firmware, such as the BIOS or UEFI, and can survive even a full system reinstall.

Antivirus software and security software can sometimes detect and remove less sophisticated rootkits, but most rootkits are built to evade these defenses. For particularly stubborn infections, you may need to use dedicated rootkit removal tools or perform a rootkit scan from a clean, external environment. In the case of firmware rootkits or deeply embedded kernel mode rootkits, the only reliable solution may be to reflash the firmware or completely wipe and reinstall the operating system.

Because rootkit removal is so challenging, prevention and early detection are critical. Regularly updating your security software and running rootkit scans can help catch threats before they become deeply entrenched. If you suspect a rootkit infection, act quickly to minimize damage and seek professional assistance if needed.

Final thoughts

Rootkits are a serious cybersecurity threat. Their ability to hide, override security, and control systems makes them particularly dangerous for individuals and organizations alike. Understanding how they work and how to defend against them is essential for maintaining a secure digital environment.