What Is a Rootkit and How Do You Remove It?

Nikolina Cveticanin

Updated: July 14, 2023

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In your time on the internet, you may have heard the term “rootkit” used in relation to nefarious activities. If you’re like most computer users, you’ve heard of it but don’t really know what it is. But what is a rootkit, exactly? And how do they work?

A rootkit is malware that hides deep within your computer system, allowing cybercriminals to access and control your machine. In this article, we’ll give you a basic rootkit definition and explain how this malware works, as well as some tips on protecting yourself from them.

What Are Rootkits?

A rootkit is a type of software that allows an attacker to gain access to and control a computer system without being detected. A rootkit can be used to backdoor a system, allowing the attacker to remotely access and control the system as if they were its legitimate owner. Rootkits are often used to steal sensitive information or launch attacks on other systems.

They’re called “rootkits” because they typically allow the attacker to gain root or administrator-level access to the system, which gives them complete control over it. The term comes from Unix and Linux OS, where the most privileged account administrator is called “root.” The “kit” part refers to the programs giving unlawful root or admin-level access to the device.

Rootkits can be used for various purposes, including data theft, espionage, and denial-of-service attacks. In many cases, rootkits are used to create “botnets,” which are networks of computers that can be controlled remotely and used to launch attacks or distribute infected files on a mass scale.

What Makes Rootkits So Dangerous?

Rootkits are notoriously difficult to detect and remove, as they often disguise themselves as legitimate files or system components. They usually operate from within the kernel of the OS, allowing them to initiate commands to the PC without the user’s knowledge.

Rootkits can disable security software, rendering themselves even harder to disable. They typically use sophisticated methods to conceal themselves, making it hard for even experienced security professionals to find and remove them.

They can also persist even if you reinstall the operating system, which makes them even more challenging to get rid of. Once a rootkit is on your system, the attacker has complete control over it.

Types of Rootkits

Rootkits come in many shapes and sizes, but they all have one common goal: To give the attacker access to and control over the target system. They are divided into five categories, depending on where they are hiding and how deeply they infect your machine.

User Mode Rootkits

A user mode rootkit is malware meant to conceal the existence of specific processes or applications from regular system users. It’s designed to attack the user processes instead of the kernel or hardware.

A user mode rootkit exists as a malicious DLL file that gets injected into a legitimate process. Once this DLL is injected, it can be used to monitor keystrokes, disable antivirus software, give remote access to an attacker, etc. It is more difficult to detect as it exists within a legitimate process and runs with the same privileges as the process it has been injected into, performing any actions that process is allowed to.

Detection of user mode rootkits can be done by analyzing the behavior of processes running on the system. If any process is found to be suspicious, then it can be further analyzed for rootkit infection. Another way of detecting user mode rootkits is by examining the system calls made by processes. If any process makes unusual system calls, it can be a sign of rootkit infection.

Kernel Mode Rootkits

Kernel mode rootkit attacks are extremely dangerous because they allow an attacker to control the entire operating system. They do this by altering the system call table or interrupt table to point to their own malicious code. This allows them to intercept system calls or interrupts and perform any actions they want.

Changing a kernel code isn’t easy, so system instability is one of the tell-tale signs of infection. Other than that, you will have a hard time detecting it. Once the rootkit is installed, you will no longer have control over your PC. You will just be a user and be able to view what the malware permits you to see, including false clean security results.

Kernel mode rootkits are very difficult to remove because they have complete control over the operating system. The only way to ensure the rootkit is gone is to format your hard drive and reinstall the operating system. This will delete everything on your hard drive, so make sure you have backups of your important files before you proceed.

Firmware Rootkits

Firmware rootkits work by creating a persistent image on hardware, such as a router, network card, hard drive, or the system BIOS. This image is then used to load and execute malicious code without the user’s consent or knowledge.

This type of rootkit is challenging to detect and remove because firmware is not usually inspected for code integrity. Even if your security software detects and removes it, there is a good chance that the malware will reappear as soon as you restart your computer.

Just like the rest of the rootkits, they can spy on you, redirect network traffic, disable devices, take control, etc. What’s intriguing about firmware rootkits is that some hardware comes preinstalled with malware; don’t worry, it’s for your protection, or so the story goes.

Absolute CompuTrace and Intel Active Management Technology use genuine rootkits functioning as anti-theft technology systems but were turned malicious under lab conditions. Intel fixed its exploit with the introduction of the Q45 chipset, but the exploit is still possible with older Q35 chipsets.

Bootkits

Bootkits are a type of malicious software that targets the Master Boot Record (MBR) located on the physical motherboard of a computer. Attaching malicious software to the MBR can allow a malicious program to be executed before the operating system is loaded.

This makes rootkit detection exceedingly difficult since all malware components exist outside the Windows system files, making it nearly impossible to detect using standard protection systems.

Bootkit infections are on the decline with the increased adoption of modern operating systems and hardware that utilize Unified Extensible Firmware Interface (UEFI) and Secure Boot technologies.

Virtual Rootkits

The virtual rootkit exploits hardware virtualization features and hosts the victim’s operating system as a virtual machine. Such a setup allows the rootkit to intercept all the hardware calls made by the original OS. Unlike most rootkit attacks, it doesn’t have to be loaded before the OS or make any modifications to the kernel.

In the simplest terms, rootkits trap your original OS in a virtual machine and intercept all traffic going from it to your PC hardware and vice versa, which places the rootkit in total control of your device.

How Does a Rootkit Work?

In some ways, a rootkit is similar to any other kind of malware. It also comes with its own trigger, installation, and self-replication mechanism, intending to steal, disrupt, cause financial harm, or extort funds.

Most rootkits work by taking advantage of vulnerabilities in the operating system to insert themselves into it. Once installed, they can then be used to hide other malicious software, disable security features, or take complete control of the system.

Rootkit malware uses a combination of two programs to install themselves onto victim computers: droppers and loaders.

The dropper will not start operating on its own after being downloaded. The user must activate it. As a result, hackers will attempt to disguise the malware or attach it to a legitimate executable file to increase the likelihood of the user running it. When the dropper is launched, it wakes the loader, which exploits system vulnerabilities and installs the rootkit.

A rootkit can be installed in several ways, including:

• Through a user action, such as visiting a malicious website.
• By exploiting a vulnerability in an application or the operating system
• By infecting another program run on the system, such as a game or media player
• Tricking users into downloading and running the program via social engineering. 

How to Detect Rootkits

A rootkit is malware designed to hide itself and other malicious software on a victim’s computer. By their very nature, rootkits are difficult to detect. However, there are a few symptoms whose unexplained occurrence may indicate the presence of a rootkit in your system.

1. Changes to system settings or files: Rootkits can be used to modify system settings and files to hide themselves or other malicious software on your system.
2. Crashes or errors: Rootkits can cause instability in your system by implanting their code at the kernel level and attempting to hide from detection.
3. Network activity: A rootkit virus can be used to steal sensitive information or launch attacks on other computers on the same network.
4. Decrease in performance: Rootkits can use valuable system resources to hide themselves or other malicious software on your system.
5. Presence of new files or programs: If you notice any new files or programs, it may be due to a rootkit installing other malicious software on your system without your knowledge.

If you suspect your system may have been infected with a rootkit, it is vital to run a malware scan as soon as possible. A malware scanner can identify and remove rootkits that may be present in your system. However, certain malware might infect and interfere with your security scan, which makes detecting rootkits much more difficult.

If you have already noticed one of the above-mentioned signs but aren’t sure why, you should look into it further, even if your anti-malware protection comes back clean. It could be a wild goose chase, but it’s better to be safe than sorry.

1. Check for unusual process behavior: This involves looking for processes behaving in ways not usually associated with their legitimate operations. This can be difficult, as there is a lot of variation in what is considered normal behavior.
2. Check for files that are not where they are supposed to be: This involves looking for files that have been moved or deleted from their usual location. This can be difficult, as rootkits can be designed to hide files.
3. Monitoring system calls: This involves monitoring the system calls being made by processes on the system. This can be difficult, as rootkits can be designed to intercept system calls.
4. Checking for unusual registry behavior: This involves looking for changes in the Windows Registry that cannot be explained. This can be difficult, as rootkits can be designed to hide changes in the registry.

How To Get Rid of Rootkits

Once you are certain your system is infected with a rootkit, you need to take immediate action to remove it. There are several things that you can try with varying degrees of success, depending on the type of rootkit.

Anti-Malware Software 

The best and easiest way to remove a rootkit is to use a malware removal tool. A good malware removal tool can scan your system for rootkits and other malware and remove them safely.

Suppose you already had anti-malware protection software which failed to prevent the initial rootkit virus attack. In that case, you may want to replace it with top-of-the-line anti-malware protection. From our own experience, Malwarebytes is quite effective in rooting out rootkits.

To have the best chance of ridding yourself of this menace, you should boot in safe mode, try to run the software, and hope for the best. As you saw in our previous section, some types of rootkit can be quite hard to eliminate. 

Bootable Anti-Malware Software

Another option is to use a bootable anti-malware CD or USB drive. This will allow you to run a scan from a clean environment and hopefully be able to remove the rootkit before it interferes with the scan. 

This rescue disk, usually a USB or a CD, includes everything you need to remove a rootkit from your computer. When you boot from the recovery CD, anti-malware software will search your computer for all types of malware and attempt to eradicate them. Most, if not all, major anti-malware companies offer this service for free, so it doesn’t cost you extra to try it.

Full HDD/SDD Wipe

In some cases, you may not be able to remove the rootkit using any of the above methods. If this is the case, your only option may be to format your hard drive or solid-state drive and reinstall the OS.

You can try to backup your data on an external device, but there is a chance you’ll preserve the rootkit as well. Be sure to run all the files through anti-malware software and watch for any signs of strange behavior when you move the files back to your freshly installed OS. 

Professional Help

If none of the above methods work for you, it’s time to seek professional assistance in removing the rootkit. Be sure to let the expert know that you think you have a rootkit so they can take the appropriate steps to ensure they do not infect their own system.

How to Prevent Rootkits

The best way to protect your computer from rootkits is to use a good anti-malware program and keep it up to date. A good anti-malware program can detect and remove most rootkits before they can cause any damage.

Don’t forget to keep your system and other programs up to date as well. Like any other malware, rootkits will exploit any system vulnerability.

You should also be careful about the programs you download and install. Only download programs from trusted sources, and be sure to read the reviews before installing anything. If you have any doubts, run the files via an anti-malware application first, or use the Virustotal website to verify the files before executing them. 

Rootkits severely threaten your computer’s security and should not be taken lightly. You should err on the side of caution whenever you have any doubts. If you think you may have a rootkit, take action immediately to remove it and protect your computer from further damage.