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If you suspect malware on a Windows PC, update Microsoft Defender security intelligence and run a full scan. Review any detection and choose an appropriate action; do not allow a file unless you trust it. If the problem persists or returns, run Microsoft Defender Offline. Consider recovery or a clean Windows installation only if scanning does not resolve the issue or Windows will not start.
Do unusual symptoms mean your PC has malware?
Not necessarily. Pop-ups, browser redirects, slow performance, or unexpectedly high data use can occur with malware, but they can also have other causes. Treat them as reasons to investigate, not proof of infection. Start with a scan rather than disabling security features or installing several antivirus products.
- Keep Microsoft Defender real-time protection enabled. Turning it off leaves files you open or download unscanned.
- Do not add broad exclusions as a cleanup shortcut: Defender will stop checking excluded items.
- Avoid running multiple real-time antivirus products at once; Microsoft warns that this can affect performance and stability.
How do you scan a Windows PC for malware?
Microsoft recommends a virus scan when you suspect infection. Menu labels can vary by Windows version, but on Windows 11 the usual route is Start > Settings > Privacy & security > Windows Security > Virus & threat protection. On Windows 10, open Settings > Update & Security > Windows Security, then choose Virus & threat protection.
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- Open Virus & threat protection and select Protection updates or Check for updates to update security intelligence. Use the update option shown in your version of Windows Security.
- Return to Virus & threat protection, select Scan options, choose Full scan, and start the scan.
- Let the scan finish, then review its result and any detected threats in Windows Security.
A quick scan checks common locations and is faster; a full scan checks every file and program, so it can take longer and slow the PC while running. If you only need to check a particular file or folder, right-click it in File Explorer and choose the Microsoft Defender scan option.
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What should you do if Windows Security detects a threat?
Open the detection details and Protection history in Windows Security to see what Defender found and what action it took. The available actions have different consequences:
- Quarantine: blocks the detected file by moving it to a safe location.
- Remove: deletes the detected item.
- Allow: permits the file to run and suppresses later alerts. Choose this only if you trust the file and its publisher.
If Windows Security reports that a threat was only partially removed, some associated malware files may remain. Follow up with another full scan and further troubleshooting; Microsoft also points to the Malicious Software Removal Tool and, when needed, Microsoft Defender Offline. Do not treat a partial-removal notice as confirmation that cleanup is complete.
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When should you run Microsoft Defender Offline?
Use an offline scan if malware keeps returning, a normal scan cannot resolve the issue, or you are concerned that malware could interfere with scanning inside Windows. Defender Offline restarts the PC and scans in the Windows Recovery Environment without loading normal Windows, which makes it harder for persistent malware to hide.
- Save open work, since the scan restarts your PC.
- In Windows Security, open Virus & threat protection > Scan options, select Microsoft Defender Offline scan, then start the scan.
- Allow the PC to restart and complete the scan and subsequent restart.
- After Windows returns, open Protection history to review the results and any action taken.
When should you use Windows recovery or reinstall Windows?
Move to recovery only if scans have not resolved the problem or Windows will not start. Microsoft’s recovery guidance describes options such as System Restore, resetting the PC, and reinstalling Windows; the available choices and their effects depend on the option and Windows version. A clean installation from Windows installation media is a last-resort option that may remove malware from the Windows installation, but it also removes Windows, personal files, apps, and settings from the selected drive.
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- Back up important files before recovery if you can. For restoring files afterward, prefer backups made before the suspected infection and stored externally; a backup or restored file is not automatically guaranteed safe.
- If Windows will not start and built-in recovery options fail, you may need to create Windows installation media using another working PC. A manufacturer recovery image may include device-specific drivers and factory apps.
- If the computer is managed by your workplace or school, contact IT before running recovery or reinstalling.
Microsoft’s guidance is to scan first. It states: “If you suspect your device has been infected, first try running a virus scan using Windows Security (Settings > Privacy & security > Windows Security).”
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How can you reduce the risk of another infection?
- Keep Windows, your browser, and other apps updated.
- Leave real-time protection enabled and scan unexpected downloads or files when appropriate.
- Be cautious with unfamiliar downloads and unexpected email attachments.
- Use built-in protections such as Windows 11 Smart App Control and Microsoft Edge SmartScreen where available, but do not assume any one feature can prevent every infection.
These steps reflect Microsoft guidance for Windows 10 and Windows 11; exact menus and feature availability may differ by version.
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Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errors
