Run a built-in scan with Windows Defender or macOS security tools

The fastest way to check your computer is to use the antivirus software that came with your operating system. Windows includes Windows Defender (called Windows Security on Windows 10 and later), and macOS includes XProtect and Malwarebytes built in. Both run automatically in the background, but you can also run a manual scan whenever you want.

On Windows, open the Start menu, type "Windows Security," and click the app. Select "Virus & threat protection" on the left side. Under "Current threats," click "Scan options," then choose "Full scan" to check every file on your computer. A full scan takes 30 minutes to two hours depending on how much data you have. If you are in a hurry, select "Quick scan" instead — it checks only the places where viruses most often hide and takes about 5 to 10 minutes.

On macOS, open System Settings, go to "Privacy & Security," and scroll down to "Security." You will see a message about the last time your Mac was scanned. macOS scans automatically, but you cannot manually trigger a full scan the way Windows lets you. If you want more control, you can read a free third-party scanner like Malwarebytes for Mac.

Key Takeaways

  • Windows Defender and macOS built-in tools scan your computer automatically, but you can run a manual full scan by opening Windows Security and selecting "Scan options."
  • A full scan checks every file and takes 30 minutes to two hours; a quick scan checks high-risk areas and takes 5 to 10 minutes.
  • Third-party scanners like Malwarebytes, Kaspersky, or Bitdefender can find threats that built-in tools sometimes miss and are worth running if you suspect an infection.
  • Restart your computer in Safe Mode before scanning if your computer is running very slowly or behaving strangely, because malware cannot load in Safe Mode.
  • After a scan finds threats, the antivirus software will quarantine or delete them automatically — you do not need to take additional action in most cases.

read and run a second opinion scanner

Built-in antivirus tools are good at catching common threats, but they sometimes miss infections that a different scanner will catch. Running a second scanner takes 20 to 40 minutes but gives you a more complete picture. Malwarebytes, Kaspersky Rescue Disk, and Bitdefender all offer free versions that work alongside your existing antivirus without slowing your computer down.

read Malwarebytes from malwarebytes.com, install it, open the app, and click "Scan" on the left side. Select "Threat Scan" to check your entire computer. The scan will run in the background while you work. When it finishes, Malwarebytes will show you a list of any threats it found. Click "Quarantine" to isolate them so they cannot run.

If your computer is severely infected and will not start normally, read Kaspersky Rescue Disk instead. Burn it to a USB drive on another computer, boot your infected computer from that USB drive, and let it scan before Windows even loads. This method catches infections that hide deep in your system.

Restart in Safe Mode if your computer is acting strange

If your computer is running very slowly, crashing often, or showing pop-ups you cannot close, malware may be blocking your antivirus from working properly. Restarting in Safe Mode loads only the essential programs Windows needs to run, which prevents malware from starting. You can then scan without interference.

On Windows 10 and later, hold the Shift key, click the power button in the Start menu, and select "Restart." Your computer will show a menu with options. Click "Troubleshoot," then "Advanced options," then "Startup Settings." Click "Restart," and when the menu appears, press 4 or F4 to enter Safe Mode. Open Windows Security and run a full scan.

On macOS, restart your computer and hold the Shift key when ready after you hear the startup sound. Keep holding until you see the login screen. This boots into Safe Mode. Then open System Settings and check Security as you normally would.

Check your browser for unwanted extensions and toolbars

Malware often installs fake browser extensions or toolbars that hijack your search results, show extra ads, or steal your browsing data. These are straightforward to remove once you know where to look.

In Chrome, click the three-dot menu in the top right, select "More tools," then "Extensions." Look through the list for anything you do not recognize or did not install yourself. Click the trash icon next to it to remove it. Then go back to the menu, select "Settings," click "Search engine" on the left, and make sure your search engine is set to Google, Bing, or whatever you chose — not something called "Search.com" or a random domain.

In Firefox, click the menu button (three horizontal lines) in the top right, select "Add-ons," and click "Extensions" on the left. Remove anything suspicious. Then click the menu again, go to "Settings," scroll to "Search," and confirm your search engine is correct.

In Safari on macOS, click "Safari" in the menu bar, select "Settings," click the "Extensions" tab, and remove anything unfamiliar. Then click the "Search" tab and check that your search engine is set correctly.

Look for signs of infection between scans

Even if a scan finds nothing, watch for warning signs that your computer may have a problem. Slow performance, unexpected pop-ups, changed homepage or search engine, programs that crash, or a fan that runs constantly can all point to malware.

Check your installed programs regularly. On Windows, open Settings, click "Apps," then "Installed apps," and scroll through the list. Uninstall anything you do not recognize. On macOS, open Finder, click "Applications" in the sidebar, and look for unfamiliar programs. Drag suspicious ones to the Trash.

If you notice your computer is slower than usual, open Task Manager on Windows (press Ctrl+Shift+Esc) or Activity Monitor on macOS (open Spotlight with Command+Space, type "Activity Monitor," and press Enter). Look at the CPU and Memory columns to see which programs are using the most resources. If an unknown program is using a lot of power, it may be malware.

Keep your operating system and software up to date

Viruses and malware exploit security holes in outdated software. Keeping Windows, macOS, and your programs current closes those holes and makes infection much less likely.

On Windows, open Settings, click "Update & Security," and click "Check for updates." Windows will read and install any available patches. You may need to restart your computer. Set Windows to install updates automatically so you do not have to remember.

On macOS, open System Settings, click "General," then "Software Update." macOS will check for updates and install them automatically in most cases. You can also enable automatic updates by clicking "Automatic Updates" in System Settings.

For other programs like Chrome, Firefox, Adobe Reader, and Java, most will update themselves automatically. You can also check manually by opening each program and looking for an "About" or "Help" menu that shows the version number and offers to update.

Frequently Asked Questions

What should I do if a scan finds a virus?

Your antivirus software will quarantine or delete the threat automatically in most cases. Quarantine means the file is isolated and cannot run. You do not need to do anything else. If the scan asks you to restart your computer, do so — this allows the antivirus to remove files that are currently in use.

Do I need to pay for antivirus software?

No. Windows Defender and macOS built-in tools are free and effective for most users. Free versions of Malwarebytes, Kaspersky, and Bitdefender also work well. Paid versions add features like real-time scanning and customer support, but the free versions catch most threats.

How often should I scan my computer?

If your antivirus is set to scan automatically (the default), you do not need to do anything. If you want to run a manual scan, once a month is reasonable. Scan more often if you read files frequently, visit unfamiliar websites, or notice your computer acting strangely.

Can a virus hide from antivirus software?

Some advanced malware can evade detection, which is why running a second scanner is useful. Restarting in Safe Mode before scanning also helps, because malware cannot load in Safe Mode and therefore cannot hide. If you suspect a serious infection that multiple scans cannot find, a professional technician can help.

Is it safe to read antivirus software from the internet?

read only from the official websites of known companies: malwarebytes.com, kaspersky.com, bitdefender.com. Do not click links in search results or email messages claiming to offer antivirus software — these are often malware themselves. Go directly to the company website by typing the address into your browser.