Boot Sector Virus: How They Work, and How to Protect Yourself

Boot Sector Virus

Boot Sector Virus: How They Work, and How to Protect Yourself

Key Points

  • Boot sector viruses were one of the earliest forms of viruses and are no longer as common as they once were.
  • Although they mainly infected floppy discs in the past, they are capable of infecting a system via USB devices. These forms of removable media should be removed when a system is shut down.
  • Because these viruses can travel via email attachments it is important to avoid opening emails from unknown senders or clicking on strange links.

What Is a Boot Sector Virus?

Viruses can be a nightmare for computer users. The nastiest programs destroy data and render your computer useless. While not as common as they used to be, boot sector viruses represent some of the earliest malware. These dangerous programs developed when more users worked with physical media like floppy disks to start their systems.

A boot sector virus gets its name from the section of a floppy disk that it infects, the boot sector. Its placement in this sensitive area allows it to infect the operating system. Because the boot files run before antiviral precautions, these viruses can circumvent some security software.

floppy disks
A floppy disk is not required to be bootable in order to transmit the boot sector virus.

How Does a Boot Sector Virus Work?

There are two related types of boot sector viruses. The original generation traveled between computers through physical media like disks and USB devices. If a computer booted up with the infected media attached, the virus could spread to the operating system.

Modern variations of the boot sector viruses will infect the master boot record of a computer’s hard drive. Every time the computer boots up, the virus can carry out its instructions.

Here is a quick video to further explain what a boot sector virus is and how it works:

What Are the Origins of Boot Sector Viruses?

A 15-year-old student created the first boot sector virus in 1982. The Elk Cloner virus was specific to the Apple II computer and its Apple DOS 3.3 operating system. This first virus was a non-malicious program that would display a poem on every 50th boot of the computer.

Within a few years, programmers created new viruses as they discovered vulnerabilities in operating systems. Malicious programs started to reformat hard drives, hijack email platforms or render the computer unbootable.

What Are the Symptoms of a Boot Sector Virus?

Because the boot sector controls startup functions, it can be difficult to recognize when a computer is infected. The oldest of these viruses were not intentionally malicious but were products of amateur programmers who wanted to showcase their abilities. These programs typically displayed a signature message during the bootup phase.

However, any alterations to the boot sector can bring serious dangers. Users may notice a sudden change in operation. The unit may be unable to carry out critical functions like starting up and connecting to the hard drive. Other viruses may start up unwanted programs during the boot process. For example, an infected computer could send malicious emails to the user’s contact list.

Examples of Boot Sector Viruses

Boot sector viruses represent some of the earliest programs designed to attack and infect personal computers. While early examples of the programs were typically not dangerous, malicious programmers used the underlying strategy to carry out damaging attacks.

Elk Cloner

Richard Skrenta, a 15-year-old student in Pennsylvania, developed the Elk Cloner virus as a prank for his friends in 1982. The program attacked the Apple DOS 3.3 operating system but had few symptoms. Once every 50 reboots, the computer would display a poem written by Skrenta. The program spread quickly because antivirus protection was not available.


In 1987, the Stoned virus appeared for the first time in New Zealand. During the boot process, infected computers would periodically display the phrase, “Your PC is now Stoned!” Although the program was non-malicious, it did bring some dangers. The program would overwrite the boot sector of floppy disks with more than 96 files in their boot directories, often rendering the disk unbootable.


The Michelangelo virus received international attention when it came to light in 1991. This program infected the boot sector so that the operating system would reformat the hard disk if a user booted up the computer on March 6. Although the virus damaged some computers on that date, media coverage allowed users to seek protection by installing antivirus software.

Keys to Boot Sector Virus Protection

Flash memory vs RAM
Boot sector viruses can be spread via USB storage devices

The first boot sector viruses relied on users sharing physical media between computers. The most common means of infection were floppy disks that contained startup instructions. Currently, USB storage devices are most likely candidates for spreading this type of malware. Users can avoid the dangers of boot sector viruses by removing media when shutting down the system. Because the malicious programs run at startup, disconnecting the media offers some protection. It is also critical to avoid inserting media from unknown sources.

Users can avoid other boot sector virus variations by using typical security precautions. These programs can travel as email attachments, so users should refrain from opening emails from unknown senders and avoid clicking on unsolicited attachments.

The latest security software can also recognize and block viruses before they can cause problems. Individuals and organizations should always use the latest versions of their antivirus programs. Allowing these security resources to update automatically will prevent attacks from the newest malware.

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02/23/2024 11:52 pm GMT

Tips for Boot Sector Virus Removal

Users that experience the symptoms of a boot sector virus may be frustrated. In many cases, the virus makes the computer unbootable. Security software companies have developed several tools to remove viruses from the boot sector without damaging other files. The user may need to boot the system using a clean system disk or USB. Once the system works, antiviral software can then begin the removal process.

In some situations, advanced users can restore the boot sector using the DOS SYS command. However, it is simpler to allow a specially-designed security tool to perform the operation for complete removal.

Are you interested in learning about other computer viruses? Check out our complete guide!

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Frequently Asked Questions

What is a boot sector virus?

A boot sector virus is a type of malware that infects the boot sector of floppy disks and other media. Other versions target the Master Boot Record of hard disks. Once infected, the program will run its instructions before the startup process is complete. This strategy helps it avoid many security measures.

How do I scan for a boot sector virus?

Antivirus software is the easiest way to search for a boot sector virus. Malicious boot sector programs often leave unique signs when they rewrite data.

What does a boot sector virus do?

Boot sector viruses insert code into the startup section of a disk. Once infected, the disk may become unbootable. Some viruses overwrite files or force hard drives to reformat.

What is boot sector virus protection?

The best protection practices for boot sector viruses are the same for other malware threats. Users should not put media from unknown sources into their computers. They should also avoid opening emails from unknown senders and unsolicited attachments.

Who created the boot sector virus?

The Elk Cloner virus is one of the earliest examples of a boot sector virus. Richard Skrenta, a 15-year-old Pennsylvania student, developed the program as a prank in 1982.

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