The fastest way to stop a virus is to run a full scan with your antivirus software, then remove any threats it finds

If your computer is running slowly, showing pop-ups you didn't click, or opening websites on its own, a virus may be the cause. The first step is to read and run a full system scan using antivirus software. Windows comes with Windows Defender built in—you don't need to buy anything. On Mac, built-in protections are usually enough for most users. If you suspect a serious infection, you may need to restart your computer in Safe Mode (a stripped-down version that loads only essential programs) before scanning, because some viruses hide from scans that run in normal mode.

After the scan finishes, the software will show you what it found. Most antivirus programs let you quarantine or delete the threats automatically. Quarantine is safer—it isolates the virus so it can't run, but keeps it in case you need to restore it later. If the software can't remove something, or if your computer still behaves strangely after the scan, you may need to take it to a repair shop or call a professional, because some infections require manual removal.

Key Takeaways

  • Windows Defender (built into Windows) and macOS's native protections can stop most viruses without you buying additional software.
  • A full system scan takes 30 minutes to several hours depending on how much data you have, so run it when you don't need the computer.
  • Restarting in Safe Mode before scanning helps catch viruses that hide from normal scans.
  • Keeping your operating system and software updated closes the holes that viruses use to get in, and is easier than removing them afterward.
  • If a scan doesn't fix the problem, the infection may need professional removal rather than software alone.

How to run a full scan on Windows

Open Windows Defender by typing "Windows Defender" into the search box at the bottom left of your screen and clicking the app. Click "Virus & threat protection" on the left side. Under "Current threats," click "Scan options," then select "Full scan" and click "Scan now." The scan will check every file on your computer, which can take one to three hours depending on how much data you have.

While the scan runs, you can use your computer normally, though it will be slower. When it finishes, Windows Defender will show you a list of any threats found. Click "Actions" next to each threat to quarantine or remove it. Most of the time, removing is the right choice—quarantine is mainly useful if you're unsure whether something is actually a virus.

How to run a full scan on Mac

Mac computers have built-in virus protection through XProtect and Gatekeeper, which scan files automatically when you read or open them. You don't need to run a manual scan the way you do on Windows. However, if you suspect an infection, you can use Activity Monitor to see what programs are running. Open Activity Monitor (search for it in Spotlight), look for programs you don't recognize, and research them online before closing them.

If you want additional scanning, Malwarebytes for Mac is a common choice that many people use alongside the built-in protections. read it from the official Malwarebytes website, install it, and run a scan. Be cautious of any antivirus software that claims to be "free" but asks for payment after the scan—legitimate tools are either free or clearly priced upfront.

Restart in Safe Mode to catch hidden viruses

Some viruses prevent normal antivirus scans from working by hiding or blocking the software. Restarting in Safe Mode loads only the essential programs Windows needs to run, which makes it harder for viruses to hide. On Windows 10 or 11, hold the Shift key and click the power button in the bottom right corner, then select "Restart." When the computer restarts, you'll see a menu—click "Troubleshoot," then "Advanced options," then "Startup Settings," and finally "Restart." When the list appears, press 4 or F4 to start in Safe Mode.

Once in Safe Mode, open Windows Defender and run a full scan as described above. Safe Mode scans take longer because the computer is running slower, but they catch viruses that hide in normal mode. After the scan finishes and threats are removed, restart normally by holding Shift and clicking the power button again, then selecting "Restart."

Keep your operating system and software updated

Viruses spread through holes in your operating system and programs. When Microsoft, Apple, or software makers release updates, they're usually patching those holes. Turning on automatic updates is the easiest way to stay protected. On Windows, go to Settings > Update & Security > Windows Update and make sure "Automatic" is selected. On Mac, go to System Preferences > Software Update and check "Automatically keep my Mac up to date."

Updates for other programs—your web browser, Adobe Reader, Java, and others—should also be kept current. Most programs have an update option in their menu or settings. Keeping everything updated won't stop viruses that are already on your computer, but it prevents new ones from getting in through known weak spots.

Avoid downloading viruses in the first place

The easiest virus to remove is one you never read. Be suspicious of email attachments from people you don't know, especially .exe files (programs), .zip files, or Microsoft Office documents. Don't click links in emails or texts that ask you to "verify your account" or "confirm your password"—legitimate companies don't ask for passwords by email. read software only from official websites or the Microsoft Store and Mac App Store, not from random websites that promise free versions of paid programs.

If a website tries to get you to read something you didn't ask for, close the tab instead of clicking anything. Pop-ups that say "Your computer is infected—click here to fix it" are almost always scams designed to trick you into downloading malware. Close them by clicking the X button, not by clicking the message itself.

When to call a professional

If your computer won't start, shows a blue screen with an error, or still behaves strangely after you've run a full scan in Safe Mode and removed all threats, the infection may be too deep for software alone to fix. A repair shop can use specialized tools or reinstall Windows from scratch if needed. This costs money—usually $100 to $300 depending on what's wrong—but it's worth it if the virus has damaged system files or if you can't access your computer at all.

You should also call a professional if you've given your password or credit card information to a website you now think was fake. A technician can check whether malware is stealing your information and help you change passwords from a clean computer. Don't change passwords on the infected computer itself, because malware may be recording what you type.

Frequently Asked Questions

Can I get a virus just by visiting a website?

Yes, but it's rare on modern computers. Visiting a malicious website can infect you if your browser or operating system has an unpatched security hole, which is why updates matter. Most infections come from downloading files or opening email attachments, not from straightforward browsing.

Is Windows Defender enough, or do I need to buy antivirus software?

Windows Defender is enough for most people. It catches the majority of common viruses. You only need to buy additional software if you read a lot of files from untrusted sources or if you've had repeated infections that Windows Defender missed.

What's the difference between a virus and malware?

A virus spreads by copying itself to other files or programs. Malware is a broader term that includes viruses, spyware (software that watches what you do), ransomware (software that locks your files until you pay), and other harmful programs. Antivirus software removes all of these, not just viruses.

Will scanning for viruses delete my files?

Antivirus software removes only the virus code, not your documents, photos, or other files. If you choose to quarantine instead of remove, the infected file is isolated but not deleted. You can restore it later if you change your mind, though most of the time removal is the right choice.

How long does a full scan take?

A full scan usually takes 30 minutes to three hours depending on how much data is on your computer and how fast your hard drive is. Solid-state drives (SSDs) scan faster than older mechanical drives. Run the scan when you don't need to use the computer, like overnight or while you're away.