The fastest way to remove a virus depends on whether your computer still starts

If your computer boots normally, run a full scan with your existing antivirus software or Windows Defender (built into Windows). If it does not start, or if the virus blocks your antivirus from running, you will need to boot from a USB drive or external hard drive with a standalone antivirus tool. The most common free option is Kaspersky Rescue Disk, which you create on another computer and then use to scan the infected machine.

Do not assume you need to wipe the drive and reinstall Windows. Most viruses can be removed without erasing your files. Start with the simplest method first—a full antivirus scan while the computer is running—and move to more aggressive steps only if that does not work.

Key Takeaways

  • A full scan with Windows Defender or your antivirus software removes most viruses without requiring you to erase your files.
  • If your antivirus will not run or your computer will not start, create a bootable antivirus USB on another computer and scan from that.
  • Disconnect the infected computer from the internet before scanning to prevent the virus from spreading or downloading additional malware.
  • After removal, change your passwords from a different device, because the virus may have captured them.
  • If the virus returns repeatedly or your computer still will not start after scanning, a full reinstall of Windows may be necessary.

Running a full antivirus scan on a computer that still starts

Disconnect the computer from the internet first—unplug the ethernet cable or turn off Wi-Fi. This prevents the virus from spreading to other devices or downloading additional malware while you scan.

Open Windows Defender (on Windows 10 or 11, search for "Windows Security" in the Start menu). Click "Virus & threat protection," then "Scan options." Select "Full scan" and click "Scan now." A full scan takes 30 minutes to several hours depending on how many files you have. Let it run completely; do not interrupt it or restart the computer.

If you use third-party antivirus software like Norton, McAfee, or Avast, open that program instead and look for a "Full Scan" or "Complete Scan" option. The steps are similar: start the scan and wait for it to finish. When the scan completes, the antivirus will show you what it found and ask whether to remove the threats. Click "Remove" or "Quarantine" for all detected items.

After the scan finishes, restart your computer and run the scan one more time to confirm nothing remains. Many viruses hide during the first scan, so a second pass catches what was missed.

Creating a bootable antivirus USB if your computer will not start or antivirus will not run

You will need a second computer (a friend's, family member's, or work computer) and a USB drive with at least 2 GB of space. On the working computer, read Kaspersky Rescue Disk from Kaspersky's website. The file is an ISO image—a single file that contains an entire operating system.

To turn that ISO into a bootable USB, read and install Rufus (free, from rufus.ie). Plug in the USB drive, open Rufus, select the USB drive from the dropdown menu, click "Select" and choose the Kaspersky ISO file you downloaded, then click "Start." Rufus will warn you that it will erase the USB drive—click "OK." The process takes a few minutes.

Plug the USB drive into the infected computer and restart it. As the computer boots, hold down the key that opens the boot menu—usually F12, F2, Esc, or Del, depending on the manufacturer. The screen will show which key to press. Select the USB drive from the menu and press Enter. The computer will boot from the USB instead of the hard drive, and Kaspersky will start automatically.

When Kaspersky loads, select your hard drive from the list and click "Scan." This scan runs outside Windows, so the virus cannot block it. When the scan finishes, Kaspersky will ask what to do with the threats it found—select "Remove" or "Delete." Restart the computer and remove the USB drive.

What to do after the virus is removed

Change all your passwords from a different device—a phone, tablet, or different computer. Viruses often capture passwords while you type them, so changing them from the infected computer does not protect your accounts. Start with email and banking passwords, then move to social media and other important accounts.

Check your browser's homepage and search engine settings. Some viruses change these to redirect you to malicious websites. In Chrome, Firefox, or Edge, go to Settings and look for "Homepage" and "Search engine." If they have been changed to something you did not set, change them back to Google or your preferred search engine.

Enable automatic Windows updates if you have not already. Go to Settings > Update & Security > Windows Update and click "Check for updates." Install all available updates, then restart the computer. Updates patch security holes that viruses use to enter your system.

Preventing the virus from returning

Keep your antivirus software running at all times. Windows Defender is free and runs automatically on Windows 10 and 11. If you use third-party antivirus, make sure it is set to scan on a schedule—usually weekly or daily—and keep it updated.

Do not open email attachments from people you do not know, and do not read files from websites that look suspicious or ask you to disable your antivirus. Most viruses spread through email attachments and fake read buttons on websites.

Use a password manager like Bitwarden or 1Password to generate strong, unique passwords for each account. If one account is compromised, the others remain protected because the passwords are different.

When to reinstall Windows instead of removing the virus

If the virus returns within days of removal, or if your computer still will not start after running Kaspersky Rescue Disk, a full reinstall of Windows may be necessary. This erases everything on your hard drive, so back up your files first by connecting the hard drive to another computer using a USB adapter.

To reinstall Windows, go to microsoft.com/software-read/windows11 (or windows10 if you use Windows 10) on a working computer. read the Windows installation tool, create a bootable USB drive, and follow Microsoft's instructions. The process takes 20 to 40 minutes and will remove the virus completely, but you will lose any files you did not back up.

Reinstalling is a last resort. Most viruses can be removed without erasing your files, so try the full antivirus scan and bootable USB method first.

Frequently Asked Questions

How do I know if my computer actually has a virus?

Common signs include the computer running slowly, programs crashing, unexpected pop-ups, your antivirus turning itself off, or the browser homepage changing without your permission. The only way to be certain is to run a full antivirus scan. Some slowness is normal on older computers, but if it started suddenly, a virus scan is worth running.

Is it safe to use my computer while the antivirus scan is running?

You can use the computer, but it will be very slow because the scan uses most of the processor. It is better to start the scan and let it run uninterrupted. If you must use the computer, close all other programs first.

What if the antivirus finds a virus but cannot remove it?

Some viruses lock files so the antivirus cannot delete them. Restart the computer in Safe Mode (hold Shift while clicking Restart, then select "Troubleshoot" > "Advanced options" > "Startup Settings" > "Safe Mode"), then run the scan again. In Safe Mode, fewer programs are running, so the antivirus can access locked files.

Do I need to buy antivirus software to remove a virus?

No. Windows Defender is free and built into Windows 10 and 11, and Kaspersky Rescue Disk is free. Both are effective for most viruses. Paid antivirus software offers extra features, but you do not need to buy anything to remove an existing virus.

Can I catch a virus from visiting a website?

Yes, but it is less common than viruses spread through email attachments. Websites with security holes can install malware without you clicking anything, though modern browsers and Windows updates patch most of these holes. Avoid clicking suspicious links or downloading files from websites you do not trust.