How to Check Your Windows PC for Viruses

Windows has a free built-in antivirus called Windows Security. Here's how to run a virus scan right now.

3 min read · 5 steps · Checked March 2026

1. Step 1. Know that Windows has free virus protection built in

   Windows 11 includes a free antivirus program called Windows Security (it used to be called Windows Defender). It runs automatically in the background. So you do not need to buy separate antivirus software. If you are still using Windows 10, you should upgrade to Windows 11 — Microsoft stopped providing security updates for Windows 10 on October 14, 2025.

   Quick Tip

   Windows Security is already installed and turned on. You do not need to download or install anything extra.

2. Step 2. Run a quick virus scan

   Click the Start button (the Windows icon in the bottom left corner). Type "Windows Security" and click it when it appears. Click "Virus & threat protection." Then click the "Quick scan" button. Windows will check the most common places where viruses tend to hide. This usually takes between 1 and 5 minutes.

3. Step 3. Run a full scan for a deeper check

   If you want a more thorough scan, go to Virus & threat protection and click "Scan options." Select "Full scan" and then click "Scan now." A full scan checks every single file on your computer. So it can take 30 to 60 minutes. It is best to start this when you will not need your computer for a while — overnight is a good time.

   Quick Tip

   A quick scan is fine for regular checkups. Use a full scan if your computer is acting strangely or you suspect a problem.

4. Step 4. Handle any threats that are found

   If Windows Security finds a virus or suspicious file, it will show you a notification with a red warning. Click "Start actions" and follow the steps on screen. In most cases, Windows will automatically quarantine (isolate) or remove the threat for you.

   Watch for these signs that your PC might have a virus: it runs much slower than usual, unexpected pop-up ads appear, your browser homepage changes on its own, new programs appear that you did not install, or your antivirus gets turned off by itself.

   Warning

   If Windows Security finds something serious, do not ignore the warning. Let it finish removing the threat, and consider changing your important passwords afterward.

5. Step 5. Keep your virus protection up to date

   Windows Security updates its list of known viruses automatically through Windows Update. To make sure this is working, click Start, then Settings, then Windows Update, and check that updates are turned on. For more help, visit support.microsoft.com and search for "Windows Security." You can also search YouTube for "How to Run a Virus Scan on Windows 11" to find a video walkthrough.