The Boot Sector Virus: What It Is and How to Remove It

An insidious virus threat to remove

A conceptual illustration of the Boot Sector virus destroying a laptop computer.

 Lifewire / Theresa Chiechi

Boot sector viruses are one of the oldest forms of computer virus out there. They infect the boot sector or partition table of a hard drive so that they're initiated the moment the computer is switched on. Here's all you need to know about them and the threat they possess. 

Boot sector viruses can affect any system with a hard drive. Primarily, PC based computers are affected most frequently, although it is possible for a Mac system to also be afflicted, as well. 

What Is the Boot Sector Virus?

A Boot Sector virus isn't a specific virus, it's a particular way in which viruses can affect your computer. A boot sector is a physical sector on your hard drive which is required to start the boot process and load your operating system. 

By placing a virus here, it means the virus is activated every time you start your computer, even before your operating system begins to boot up. Often, you won't even realize it's happening which makes the threat potentially even worse.

How Does the Boot Sector Virus Work?

Each boot sector virus works differently, depending on their aim. Because they're located on the boot sector of your hard drive, before the operating system begins, it's possible for a boot sector virus to cause a lot of damage. 

Some might just cause irritating issues like an adware or malware virus might create, but others can work as Trojans, monitoring what you're doing at all times and stealing your information in the background. Ransomware also often takes advantage of one's boot sector, holding the contents of your hard drive for ransom. 

Boot sector viruses can even spread to other hard drives you have installed or physical media you have plugged into your system. 

It's important that you delete the threat as soon as possible so that the problem doesn't get worse over time.

How Do I Know I Have the Boot Sector Virus?

Boot sector viruses aren't always obvious to spot. Often, it depends on what kind of virus you've been infected with.

Some of the most dangerous ones such as a RAT (remote access Trojan) are near impossible to detect unless the person remotely accessing your computer is clumsy with their actions. 

Others might cause regular data issues, causing your files to disappear from partitions or suddenly making your computer act unstable and crash frequently. Error messages such as 'invalid system disk' can also pop-up regularly. 

It's important to run regular antivirus software scans or use malware detection tools to spot any potential issues before they get worse. 

How Did I Get the Boot Sector Virus?

Traditionally, boot sector viruses were received via infected physical media such as a floppy disk or USB stick. Boot sector viruses typically infect the storage device's master boot record

Nowadays though, it's also possible to be infected by malware that is downloaded or received via email attachments. It's important to be vigilant about the files you download and the websites you access.

How Do I Get Rid of the Boot Sector Virus?

The best and most efficient way to get rid of the boot sector virus is to use antivirus software, as well as a malware removal app. 

Antivirus software can take a number of hours to complete the process, depending on the speed of your computer, but it also offers you the best methods in which to remove the malicious files. 

Many antivirus software tools also offer boot sector protection so that your hard drive's master boot record is protected from illicit access. In the worst-case scenario, some antivirus software also includes bootable physical media so you can remove a boot sector virus more easily. 

It's also worth installing a malware removal tool which helps detect any other malware on your system, long before it causes any substantial problems on your computer. 

Like antivirus software, malware scanning can take many hours depending on the size of your computer's hard drive, as well as its speed. 

Unlike other viruses, System Restore and reformatting the hard drive aren't effective means in which to remove a boot sector virus. 

It is possible to use a free bootable antivirus software tool to detect issues before you boot into Windows, however. 

How Can I Avoid Getting the Boot Sector Virus Again?

There are a few key ways in which you can lower your chances of being re-infected with a boot sector virus (or being afflicted with any other virus). There are also specific tips that relate directly to boot sector viruses.

  • Update your antivirus software and malware protection. Keep your antivirus software and malware protection up to date. New virus definitions are released regularly and these keep your PC informed on what to look for with new virus and malware-based threats. Good antivirus software also protects your boot sector and quickly detects if a virus is trying to interfere with it. 
  • Be wary of physical media. Be careful about what USB sticks you place on your computer. This is one of the key ways in which you can be affected by a boot sector virus. Consider the source of the USB stick before using it, and never place it in your computer before you boot up the system.
  • Be vigilant. Boot sector viruses can easily transmit between different computers on the same network. Be careful about what networks you connect your system to.
  • Don't download suspicious files. Consider where you're downloading files from and always run virus scans on them before opening them. Torrented files, in particular, can open you up to malware viruses that can lead to infecting your boot sector.