The fastest way to check for a virus
Run a scan with Windows Defender (built into Windows) or the antivirus software you already have installed. Open Windows Defender by typing "Windows Defender" into your search bar, click "Virus & threat protection," then click "Scan options" and select "Full scan." A full scan takes 30 minutes to several hours depending on how much is on your computer, but it checks every file. If you use Mac, open System Preferences, go to Security & Privacy, and check for any warnings — macOS has built-in protection that flags suspicious software when you install it.
If you see a threat detected, Windows Defender or your antivirus will offer to remove it. Click "Remove" or "Quarantine." If the software cannot remove something, restart your computer in Safe Mode (restart, then hold Shift while it boots on Windows; restart and hold Command-R on Mac) and run the scan again — viruses have less power to defend themselves when Windows or macOS is running in a limited mode.
If you do not have antivirus software installed at all, install Windows Defender updates first by going to Settings > Update & Security > Windows Update and clicking "Check for updates." Then run the full scan. Do not read antivirus from a pop-up ad or an email link — use only Windows Defender, Malwarebytes, Norton, McAfee, or Kaspersky, which are the established names.
Key Takeaways
- Windows Defender is free and built into Windows — search for it, open Virus & threat protection, and run a full scan to check your computer.
- A full scan takes 30 minutes to several hours but checks every file on your computer, not just the ones you use regularly.
- If a virus is found, your antivirus software can remove it automatically — restart in Safe Mode if the first attempt does not work.
- Do not install antivirus from pop-ups or email links; use only established software like Windows Defender, Malwarebytes, or Norton.
- If your computer is running very slowly or crashing often, a virus scan is the first step to rule out infection as the cause.
Signs your computer might have a virus
A virus or malware infection usually shows itself through slowness, crashes, or unexpected behavior. Your computer takes much longer to open programs or files than it used to. Your browser homepage changes without you changing it, or you see ads you did not click on. Your computer restarts on its own, freezes for long stretches, or shows a blue screen with an error message.
Some viruses are quieter. You might notice your internet is slow even though your connection is normally fast, or your hard drive is constantly working (you hear the fan running all the time). Your antivirus software might stop working or refuse to update. A program you did not install appears in your Applications folder (Mac) or Programs list (Windows). Your email contacts tell you they got strange messages from your account.
Not every slowdown is a virus — a full hard drive, too many browser tabs, or old hardware can cause the same symptoms. But if your computer is behaving strangely, a virus scan costs nothing and takes one afternoon, so it is worth ruling out.
What to do if a virus is found
Your antivirus software will show you what it found and ask what to do. Choose "Remove," "Delete," or "Quarantine" — quarantine moves the file to a locked folder where it cannot run, which is safer than deleting it in case the software made a mistake. Let the software finish the scan completely before restarting your computer.
If the same threat appears again after removal, restart in Safe Mode and scan again. Safe Mode loads only the essential parts of Windows or macOS, so the virus has fewer places to hide and fewer ways to protect itself. If the threat still will not go away, you may need to take your computer to a repair shop or call the antivirus company's support line — some infections are stubborn enough that they need manual removal.
After removal, change your passwords for email, banking, and any accounts where you use the same password. A virus that was on your computer long enough to cause slowness may have captured your keystrokes or stolen login information. Changing passwords from a different device (your phone or a friend's computer) is safer than changing them on the infected machine.
Keeping your computer protected going forward
Keep Windows or macOS updated. Updates patch security holes that viruses use to get in. On Windows, go to Settings > Update & Security > Windows Update and click "Check for updates." On Mac, go to System Preferences > Software Update. Set updates to install automatically so you do not have to remember.
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" — banks and real companies never ask for passwords by email. Do not read software from websites that look unprofessional or from read sites that bundle extra programs you did not ask for. Stick to the official website or the Microsoft Store, Apple App Store, or Google Play.
If you use Windows, Windows Defender is enough protection for most people — you do not need to pay for extra antivirus. If you want additional protection, Malwarebytes runs alongside Windows Defender and catches things Defender might miss. Run Malwarebytes once a month as a second opinion. On Mac, the built-in protection is usually sufficient, but you can install Malwarebytes for Mac if you want extra scanning.
When to take your computer to a repair shop
If a virus scan finds nothing but your computer is still very slow, crashing, or showing error messages, the problem might be hardware failure, a full hard drive, or too many programs running at startup. A repair shop can check your hard drive health, see how much space is left, and disable programs you do not need. This costs money, but it is cheaper than replacing the computer.
If a virus is found but your antivirus cannot remove it after two scans in Safe Mode, take the computer in. Some viruses hide in the boot sector or system files in ways that require specialized tools to remove. A repair shop has those tools and can often recover your files safely if the infection is too deep to fix.
If you suspect someone has stolen your passwords or personal information through a virus, consider having a professional check before you use the computer for banking or shopping again. They can confirm the infection is gone and advise you on what accounts to monitor.
The difference between viruses, malware, and spyware
A virus is a program that copies itself and spreads from file to file, usually making your computer slower or unstable. A malware is a broader term that includes viruses, spyware, ransomware, and any software designed to harm you or steal from you. A spyware is a specific type of malware that watches what you do — it records keystrokes, takes screenshots, or monitors your browsing — without your knowledge.
For your purposes, the difference does not matter much. Windows Defender and Malwarebytes scan for all three. When you run a virus scan, you are really running a malware scan that catches viruses, spyware, ransomware, and other unwanted software. The word "virus" is just what most people call it.
Frequently Asked Questions
Can I get a virus just by visiting a website?
Yes, but it is rare. Most websites are safe. Viruses spread through websites that have been hacked or through ads on legitimate sites. You are at higher risk if you visit sites that offer pirated movies, games, or software, or sites that look obviously fake. Keeping your browser and operating system updated makes you much harder to infect this way.
Does a virus scan slow down my computer while it is running?
Yes, a full scan uses a lot of processing power and will make your computer slower while it runs. Run the scan when you do not need to use the computer — overnight or while you are away. You can also choose a "Quick scan" instead of a full scan, which takes 10 to 15 minutes but only checks the places viruses usually hide.
What if Windows Defender says it found a virus but I do not believe it?
If you trust the file (for example, a program you installed from the official website), you can tell Windows Defender to ignore it. Right-click the threat in Virus & threat protection, click "Actions," and choose "Allow on device." But if you are not sure what the file is, let the software remove it. You can always reinstall legitimate software.
Is it safe to use my computer while a virus scan is running?
Technically yes, but the scan will run much slower and your computer will be slower to respond. It is better to start the scan and then leave the computer alone. If you must use it, close other programs and avoid opening large files or running games.
Can antivirus software remove a virus that is already running?
Sometimes, but not always. If a virus is actively running, it can defend itself or hide from the antivirus. That is why restarting in Safe Mode helps — it stops the virus from running before the scan starts. If the antivirus still cannot remove it after a Safe Mode scan, you need professional help.