Usually, you should not keep two antivirus programs’ real-time protection running at the same time. On Windows, multiple active anti-malware apps can slow or destabilize a PC. Microsoft Defender Antivirus normally turns off when a compatible third-party antivirus is installed and turned on, but check Windows Security to confirm which product is protecting your device.
Why running two real-time antivirus programs can cause problems
Real-time protection continuously monitors files and programs as they are accessed or run. With two antivirus products doing this work, their overlapping activity can affect system performance or stability. Microsoft warns that running multiple anti-malware apps at once can make a system slow or unstable: Protect my PC from viruses.
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Microsoft notes that two third-party antivirus products may both try to run at once. Installing another product does not guarantee that your existing antivirus will automatically step aside.
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On supported Windows configurations, Microsoft Defender Antivirus turns off automatically if another antivirus app is installed and turned on. Microsoft describes this behavior in its Windows Security app overview. The handoff depends on the other app being compatible and active; do not assume every antivirus installation disables Defender.
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After uninstalling the other antivirus, Defender should turn back on automatically. Confirm the status rather than relying on the expected handoff: open Windows Security and check the protection status shown for your device. Microsoft’s Virus and threat protection in the Windows Security app explains the available protection and scan options.
Is a manual second scan different?
Yes. A one-time scan of a file or folder, or an on-demand scan that you run when needed, is different from leaving two antivirus products continuously monitoring activity. Windows Security supports scans of individual files and folders. The concern is chiefly overlapping real-time protection, not every occasional scan by another tool.
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How to switch antivirus without leaving a protection gap
- Before removing your current antivirus, choose the replacement. Microsoft cautions that removing internet-security software can leave the PC unprotected unless another anti-malware product is enabled.
- Install and turn on the replacement antivirus. Allow it to complete setup so its protection can become active.
- Check Windows Security. Confirm that a protection provider is active and that the device is not reporting a gap.
- After uninstalling the old product, check again. Defender should resume automatically if no other antivirus is active, but verify its status in Windows Security.
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