How to scan your computer for viruses

The fastest way to check your computer for viruses is to run a full system scan using the antivirus software already built into your operating system. On Windows 10 and 11, that's Windows Defender (also called Microsoft Defender). On Mac, the system includes XProtect, which runs automatically in the background. Both scan your files, programs, and startup processes without you paying anything extra.

To run a manual scan in Windows Defender, open the Windows Security app (search for "Windows Security" in your Start menu), click "Virus & threat protection," then select "Scan options." Choose "Full scan" — this takes longer than a quick scan but checks every file on your drive. The scan can take 30 minutes to several hours depending on how much data you have. You don't need to do anything while it runs; you can use your computer normally, though it will be slower.

If you use a Mac, open System Settings, go to General, then select Security & Privacy. You'll see a message about XProtect running in the background. You can't manually trigger a full scan the way Windows users can, but XProtect scans files as they're downloaded and opened. If you want a more thorough check, you can restart your Mac while holding Command + R to enter Recovery Mode and run Disk Utility, though this is rarely necessary for virus detection.

Key Takeaways

  • Windows Defender and Mac's XProtect are built-in and free; running a full system scan is your first step before installing anything else.
  • A full scan in Windows takes 30 minutes to several hours and checks every file; you can use your computer while it runs.
  • If Windows Defender finds threats, it will quarantine them automatically; you can review what was found in the Virus & threat protection history.
  • Third-party antivirus software like Malwarebytes can catch things the built-in tools miss, but start with what you already have.
  • Restart your computer in Safe Mode before scanning if malware is actively interfering with your system or preventing scans from running.

Understanding what the scan results mean

When a scan finishes, Windows Defender shows you a summary. If it found nothing, your system is clean — at least as far as that scan could tell. If it found threats, the software will show you the name of each one, where it was found, and what action was taken (usually "Quarantined," which means the file was moved to an isolated folder where it can't run).

The quarantine folder in Windows Defender is called the "Quarantine" section within Windows Security. You can view what's there by opening Windows Security, going to "Virus & threat protection," scrolling down to "Virus & threat protection history," and clicking "Quarantined items." From there you can permanently delete the files or restore them if you're certain they're safe. Most of the time, you should delete them.

If the scan found malware but couldn't remove it, or if your computer is still behaving strangely after a clean scan result, the infection may be deeper than a standard scan can reach. That's when a second opinion from a different tool becomes useful.

When to use a second antivirus tool

Running two antivirus programs at the same time will slow your computer and cause conflicts, so don't do that. But running a second scan with a different tool after your first scan is complete is a reasonable next step if you're still seeing problems or if you want extra confidence.

Malwarebytes is the most common second choice. It's free to read and run a single scan, though it costs money if you want real-time protection. read it from malwarebytes.com, install it, and run a scan. Because Malwarebytes uses different detection methods than Windows Defender, it sometimes catches things the built-in tool missed. After the scan finishes, you can uninstall Malwarebytes if you don't want to keep it.

Another option is Kaspersky Rescue Disk, which is a bootable tool that scans your computer before Windows even loads. This is more thorough but also more technical — you create a USB drive with the rescue disk, restart your computer to boot from that drive, and let it scan. Use this only if you suspect serious malware that's hiding from normal scans.

Checking for viruses in Safe Mode

If your computer is running slowly, crashing, or showing pop-ups even after a normal scan, malware may be actively interfering with Windows. Restarting in Safe Mode disables most programs and drivers, making it harder for malware to hide or interfere with the scan.

To restart in Safe Mode on Windows 10 or 11, hold the Shift key and click the power button in the Start menu, then select "Restart." Your computer will show a menu; select "Troubleshoot," then "Advanced options," then "Startup Settings," then "Restart." After the restart, you'll see a list of startup options; press 4 or F4 to enter Safe Mode. Once you're in Safe Mode, open Windows Defender and run a full scan the same way you normally would.

Safe Mode loads only essential system files, so the scan may take longer and your computer will feel very basic — no sound, limited graphics, no internet in some cases. That's normal. Once the scan is done, restart normally to return to your regular desktop.

Keeping your computer protected going forward

Scanning once is useful, but viruses and malware come back if you don't change your habits. The most common entry points are email attachments, downloads from untrusted websites, and fake software updates.

Make sure Windows Defender's real-time protection is turned on. Open Windows Security, go to "Virus & threat protection," and check that "Real-time protection" shows as "On." This scans files as they arrive on your computer, not just when you run a manual scan. Keep Windows itself updated by going to Settings > Update & Security > Windows Update and checking for updates regularly — many updates patch security holes that malware exploits.

Don't open email attachments from people you don't know, and be skeptical of attachments even from people you do know if the message seems odd or out of character. Don't read software from anywhere except the official website or the Microsoft Store. If a website tells you to update your browser or install a plugin, close the tab and go directly to the official site instead — scammers use fake update prompts to distribute malware.

Signs your computer might have a virus

You don't always need to wait for a scan to suspect malware. Some behaviors are red flags. If your computer is much slower than usual, especially at startup, malware may be running in the background. If you see pop-ups appearing even when you're not browsing, or if your browser homepage changed without you changing it, that's often a sign of adware or a browser hijacker.

Unexpected crashes, programs that won't open, or a fan that's constantly loud are also possible signs, though they can also mean hardware problems or normal software conflicts. If you notice any of these, run a scan — it won't hurt, and it will either find the problem or rule out malware so you can look elsewhere.

One important note: legitimate antivirus software will never ask you to pay to remove a virus it found, and it won't pop up warnings telling you to call a number. If you see a pop-up like that, it's a scam. Close the browser tab or restart your computer, then run Windows Defender from the Start menu instead.

Frequently Asked Questions

How often should I scan my computer for viruses?

If Windows Defender's real-time protection is on, you don't need to manually scan every week. Run a full scan once a month, or sooner if you notice your computer acting strangely. If you read files from untrusted sources regularly, scan more often.

Can a virus hide from Windows Defender?

Yes, some sophisticated malware can evade standard scans by hiding in parts of your system that normal tools don't check, or by disabling Windows Defender itself. If you suspect this, restart in Safe Mode and scan again, or use Malwarebytes or Kaspersky Rescue Disk as a second opinion.

What should I do if a scan finds a virus but can't remove it?

Windows Defender will quarantine it, which prevents it from running. If the same threat keeps reappearing after scans, or if your computer still has problems, the malware may be too embedded for standard tools. Consider taking your computer to a repair shop or backing up your files and reinstalling Windows.

Is it safe to read antivirus software from the internet?

read only from the official website. Go directly to malwarebytes.com or kaspersky.com in your browser, not through a search result or email link. Scammers create fake antivirus sites that actually install malware.

Do I need to pay for antivirus protection?

No. Windows Defender is free and sufficient for most users. Paid antivirus software offers extra features like VPN or password managers, but the core scanning and protection in Windows Defender is solid. Malwarebytes offers a free scan, though the paid version adds real-time monitoring.