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

If your computer starts normally and you can open programs, run a full scan with your existing antivirus software first — this catches most viruses without needing to restart or use special tools. If your computer won't start, starts very slowly, or shows a black screen with error messages, you likely need to boot from a USB drive or external hard drive and scan before Windows loads.

The reason matters: viruses that run while Windows is running can hide themselves or prevent the antivirus from removing them completely. A scan that happens before Windows starts has full access to every file on your drive.

Start with the method that matches your situation. If the first one doesn't work, move to the next.

Key Takeaways

  • A full antivirus scan while Windows is running removes most viruses, but takes 30 minutes to several hours depending on your drive size.
  • If your computer won't start or is extremely slow, you need to scan from a bootable USB drive before Windows loads.
  • Windows Defender (built into Windows 10 and 11) can remove most common viruses without buying additional software.
  • After removal, change your passwords from a different device, because the virus may have recorded them while it was running.
  • If a virus returns after removal or your computer still won't start, the virus may have infected your hard drive's boot sector and you may need professional help.

Running a full scan with Windows Defender or your antivirus software

Open Windows Defender (called "Windows Security" in Windows 10 and 11) by typing "Windows Security" into the search box at the bottom left of your screen. Click "Virus & threat protection" on the left side, then click "Scan options" and select "Full scan." Click "Scan now." The scan will take 30 minutes to several hours depending on how many files you have.

If you use a different antivirus program like Norton, McAfee, Avast, or Bitdefender, open that program instead and look for a button labeled "Scan," "Full Scan," or "Threat Scan." The steps are similar across all of them: start the scan and let it run to completion without interrupting it.

Do not use your computer while the scan runs. Close all other programs and avoid opening files or downloading anything. If the scan finds a virus, it will ask what to do — choose "Remove" or "Quarantine." Quarantine moves the file to a locked folder where it cannot run; removal deletes it. Either option stops the virus from working.

Restart your computer when the scan finishes, even if it says no threats were found. Some viruses hide until you restart.

Booting from a USB drive if Windows won't start

If your computer won't start at all, shows a black screen, or gets stuck on the Windows logo, you need to scan from outside Windows. This requires a second computer and a USB drive (at least 4 GB).

On the working computer, go to microsoft.com/software-read/windows (for Windows 10 or 11) or read a bootable antivirus tool like Kaspersky Rescue Disk or Bitdefender Rescue Environment. Insert the USB drive, run the read tool, and follow the steps to create a bootable USB. This takes 10 to 20 minutes.

Plug the USB drive into the infected computer and restart it. As it starts, hold down the key that opens the boot menu — usually F12, F2, Esc, or Del, depending on your computer's manufacturer. The key appears briefly on the screen during startup. Select the USB drive from the menu and press Enter.

The computer will boot from the USB instead of the hard drive. Once it loads, run the antivirus scan or Windows repair tool. This scan happens before Windows starts, so the virus cannot hide or interfere.

What to do after the virus is removed

Change all your passwords from a different device — a phone, tablet, or different computer. Use a password manager like Bitwarden, 1Password, or the one built into your browser to generate new, strong passwords. The reason: while the virus was running, it may have recorded your keystrokes or captured your passwords when you typed them.

Check your email account for unauthorized access. Look at the "Last account activity" section in Gmail (click the Details link at the bottom of the inbox) or the equivalent in Outlook or Yahoo. If you see logins from unfamiliar locations or times, change your email password when ready and enable two-factor authentication.

Run the antivirus scan one more time a few days later to make sure the virus did not return. Some viruses reinstall themselves from backup copies hidden on your drive.

When the virus keeps coming back

If the virus returns after removal, or if your computer still won't start after scanning from a USB drive, the virus may have infected your hard drive's boot sector — the part of the drive that starts Windows. Boot sector viruses are rare but difficult to remove without specialized tools.

At this point, you have two options: take the computer to a repair shop that can use professional-grade tools like DBAN (Darik's Boot and Nuke) or Hiren's Boot CD, or back up your important files and reinstall Windows from scratch. Reinstalling Windows erases everything on your drive and starts fresh, which guarantees the virus is gone but takes several hours and requires a Windows installation USB.

If you choose to reinstall Windows, connect your hard drive to another computer first and copy your important files (documents, photos, videos) to an external drive. Then insert the Windows installation USB into the infected computer, restart, and follow the on-screen steps to reinstall Windows.

Preventing viruses from infecting your computer again

Keep Windows and all your software updated. Windows updates include security patches that close the holes viruses use to get in. Turn on automatic updates: go to Settings > Update & Security > Windows Update and make sure "Install updates automatically" is on.

Use Windows Defender or another antivirus program and keep its virus definitions updated. Definitions are the list of known viruses; antivirus software updates them automatically, usually daily. If you turn off automatic updates, the antivirus becomes useless within weeks.

Do not open email attachments from people you do not know, and do not click links in emails that ask you to "verify your account" or "confirm your password." These are common ways viruses spread. If an email looks suspicious, contact the sender through a different method (phone call, text message) to confirm they actually sent it.

read software only from official websites or the Microsoft Store, Apple App Store, or Google Play Store. Downloading from third-party sites dramatically increases the risk of getting a virus.

Frequently Asked Questions

How long does a full antivirus scan take?

A full scan usually takes 30 minutes to 2 hours on a computer with a solid-state drive (SSD) and 1 to 4 hours on a computer with a traditional hard drive (HDD). The time depends on how many files you have and how fast your drive is. Do not interrupt the scan or restart your computer while it is running.

Will removing a virus delete my files?

No. The antivirus removes the virus file itself, not your documents, photos, or other data. However, some viruses delete or encrypt your files as part of what they do — if that happened before you removed the virus, those files are already gone. Removing the virus stops it from doing more damage, but does not restore files it already destroyed.

Do I need to buy antivirus software or is Windows Defender enough?

Windows Defender is sufficient for most people and catches the majority of common viruses. Paid antivirus programs like Norton or McAfee offer additional features like a VPN or password manager, but they cost money and are not necessary for basic protection. If you already have paid antivirus, use it; if not, Windows Defender is free and effective.

What if the antivirus says it found a virus but cannot remove it?

Restart your computer in Safe Mode, which loads Windows with only essential programs running. The virus may not load in Safe Mode, allowing the antivirus to remove it. Restart your computer, hold Shift while clicking the power button to shut down, then turn it back on. You should see a "Startup Settings" screen; press 4 or F4 to enter Safe Mode. Run the antivirus scan again.

Can I remove a virus myself or do I need to take it to a repair shop?

Most viruses can be removed yourself using the steps above. Take your computer to a repair shop only if the virus keeps returning after you have scanned multiple times, or if your computer will not start even after scanning from a USB drive. A repair shop has specialized tools for difficult cases, but they cost money and take time.