If you suspect your Windows 11 PC has picked up unwanted software, running a manual malware scan through Windows Defender is the fastest first step. Windows Security (formerly Windows Defender) comes built into every modern Windows installation, and it gives you three distinct scanning options depending on how deep you need to dig. This guide walks you through each option, explains what to expect during the scan, and shows you how to handle the results safely.
Before You Start: Make sure your PC is connected to the internet so Windows can download the latest virus definitions. If you are running a third-party antivirus, Windows Defender will pause its real-time protection automatically, and you will need to open that program instead. This guide assumes you are using the built-in Windows Security app on Windows 11.
Step 1: Open Windows Security
Click the Start button and type Windows Security, then press Enter. The Windows Security app serves as the central hub for all your system safety settings. You will see a grid of icons representing different protection categories like firewall, account protection, and device performance. If the app does not appear in your search results, open Settings, navigate to System, and select Troubleshoot > Other troubleshooters to verify the app is enabled on your system.
Step 2: Navigate to Virus & threat protection
Click the Virus & threat protection tile in the top-left corner of the Windows Security window. This section controls your malware scanning engine and quarantine settings. You will see a status bar at the top confirming whether your protection is currently active. If you see a warning banner here, Windows needs your attention before you can run a manual scan, so address any listed issues first.
Step 3: Choose your preferred scan type
Scroll down to the Current threats section and click the Scan options link. Windows Defender offers three distinct scan modes, and picking the right one depends on how much time you have and how suspicious the infection seems. The Quick scan checks roughly 200 high-risk locations and usually finishes in under fifteen minutes. The Full scan examines every file on every drive, which can take several hours but catches deeply hidden threats. The Custom scan lets you pick specific folders or drives to check, which is useful if you only suspect a particular download or external drive.
Step 4: Start the scan and monitor progress
Select your chosen scan type and click the Scan now button. Windows Defender will begin checking files and display a progress percentage at the top of the window. You can continue using your PC during a quick scan, but a full scan may slow down performance because the engine is actively reading every drive sector. If the scan pauses unexpectedly, check your power settings and make sure your PC is plugged in, as battery saver mode can throttle background security tasks.
Step 5: Review results and handle detected threats
When the scan finishes, click View threats or review the on-screen summary to see what Windows Defender found. Each detected item will list its name, severity, and the action Windows Defender already took. You can choose to remove the threat, quarantine it, or allow it if you believe the file is a false positive. If you see a prompt asking whether to take action, select the recommended option and confirm with Yes. Quarantined files are isolated from your system and can be restored later if needed.
Troubleshooting common scan issues
If the scan refuses to start, check for conflicting security software. Running two real-time antivirus programs simultaneously will cause Windows Defender to disable itself. Open your third-party antivirus settings, temporarily pause protection, run the Windows scan, and then re-enable your other program. If the scan runs but finds nothing despite clear symptoms, try booting into Safe Mode and repeating the full scan. Malware often hides in startup folders and active memory, which Safe Mode leaves unloaded. If Windows Defender is completely grayed out, run a system file check by opening Command Prompt as administrator and typing sfc /scannow. This repairs corrupted system files that sometimes break the security app. If you receive error code 0x80070005 during the scan, your account lacks administrative privileges. Sign out, log back in with an administrator account, and try again.
Pro Tip: Keep your virus definitions updated by clicking Check for updates under Virus & threat protection settings. Outdated definitions are the number one reason manual scans miss modern threats.
Quick Tip: You can schedule automatic scans by returning to Scan options and toggling Scheduled scan to On. This removes the need to remember manual checks in the future.
Running a manual malware scan takes less than five minutes of your time and gives you immediate peace of mind. Windows Defender handles the heavy lifting in the background, and following these steps ensures you catch threats before they cause lasting damage. If you run into any unexpected prompts during the process, leave them alone and consult official Microsoft support documentation before taking action.
What is the most common sign of malware you have noticed on your Windows PC, and did a manual scan catch it?
Over to you: What is the most common sign of malware you have noticed on your Windows PC, and did a manual scan catch it?
