Think of Unknown/Uncommonly downloaded warnings as an early warning system for potentially undetected malware. With almost 2 billion websites on the internet and software continuously updated and released, it's impossible to have information about every single site and program. It takes time to identify and block malicious sites and applications, or trust newly released programs and certificates.

No antivirus or protection technology is perfect.

The following list may not be comprehensive, and Microsoft reserves the right to adjust, expand, and update these without prior notice or announcement. In some instances Defender may need you to take some actions such as quarantining or removing the dangerous file or process.New forms of malware and potentially unwanted applications are being developed and distributed rapidly. If Defender finds malware on your device it'll block it, notify you, and try to remove the malware if it can. For more information see How to start a scan for malware in Microsoft Defender What if Defender finds malware? If you're concerned and want to have Microsoft Defender run a scan right now, you can do that by going to the Device protection page from the Microsoft Defender dashboard. If it spots something it will attempt to block it, and alert you so that you can take action if necessary.

Microsoft Defender will also run quick scans of your device on a daily basis, in case anything manages to elude the real-time protection. Microsoft Defender's real-time anti-malware protection runs whenever your device is on, keeping an eye out for malicious activity. When you first set-up Microsoft Defender on your device we'll run an initial scan to make sure you're starting off clean. Note: Microsoft Defender currently offers anti-malware only on Windows, Mac, and Android.

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