On Windows, start with the free Microsoft Defender Antivirus already included in Windows Security: update its security intelligence, then run a full scan for a deliberate check of your files and programs. A clean result is useful, but it is not proof that a device is malware-free. The steps below are for Windows; Android needs a separate, Android-specific assessment.
How do I scan my Windows PC for viruses for free?
Microsoft Defender Antivirus is built into Windows Security. Microsoft documents both quick and full scans; for a more thorough check, update security intelligence first and then run a full scan.
- Open Windows Security: Open Start, search for Windows Security, and launch it.
- Check protection and updates: Select Virus & threat protection. Confirm that protection is on. If the option is available, update security intelligence before scanning.
- Run an initial check: Select Quick scan for a faster first pass. To check more thoroughly, open Scan options, choose Full scan, and start the scan. A full scan is the appropriate choice when you want Windows to check files and programs across the system. Microsoft recommends getting the latest security intelligence and then running a full scan in its unwanted-software guidance.
- Review the result: Return to Virus & threat protection and review any detections. Follow the remediation instructions shown in Windows Security; a detection may need action, and removal is not guaranteed in every case.
Microsoft says, “Microsoft Defender Antivirus tries to block malware before it can infect your device.” A scan is one part of protection, not a guarantee that every threat will be found.
What should I check after the scan?
Keep real-time protection on
Real-time protection monitors for threats on an ongoing basis; a full scan is a deliberate check you start yourself. Check that real-time protection is enabled in Virus & threat protection. Keep Windows and security intelligence up to date so protection has current threat information.
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Avoid broad exclusions
Do not add file or folder exclusions just to silence a warning unless you understand the risk. Microsoft notes that excluded file types or locations will no longer be checked, which can leave the device and data vulnerable. See Microsoft’s explanation of exclusions.
Use SmartScreen as a companion, not a replacement
Microsoft Defender SmartScreen uses reputation-based protections to warn about websites and apps associated with phishing or malware distribution. It can help flag risky destinations and downloads, but it is a separate layer from an antivirus scan, not a substitute for one. Microsoft describes how Defender SmartScreen works.
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Does my computer already have a free virus scanner?
If you use Windows, Microsoft Defender Antivirus is included through Windows Security, so you can run a scan without installing a separate scanner. The exact interface can vary by Windows version. For this workflow, use Windows Security’s scan controls and follow the remediation guidance it presents.
A scan that reports no current threats does not certify that the computer is clean: no single scan can establish that with certainty. If Windows reports a serious detection, you cannot complete remediation, or the device continues behaving suspiciously, consider getting help from a qualified support professional.
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What about scanning an Android phone or an iPhone?
Android
Android products should be assessed using Android-specific information, not Windows rankings. AV-TEST’s July 2026 Android overview covers malware detection and usability, including performance and false positives, and includes Google Play Protect alongside third-party products. That Android evaluation does not establish which app is best for every phone or user. Check current Android-specific app details and test results before choosing a product.
iPhone
The Windows scan instructions here do not apply to iPhone. The cited information does not establish a detailed iPhone scanning procedure, so do not install or follow a Windows antivirus workflow on an iPhone based on this guide.
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How should I compare free antivirus products?
Do not choose a product from a detection percentage or a “best” label alone. Independent test results apply to a particular product version, platform, test period, and configuration. For each candidate, check:
- Platform and version: Make sure the test is for your operating system and identifies the product version.
- Test date and settings: Prefer recent results and note whether the lab used default settings or another configuration.
- Protection: Review how well the product detected and blocked threats in that test.
- Performance: Consider the measured effect on everyday system use.
- Usability and false positives: Check whether legitimate files or sites were incorrectly flagged and how the product handled warnings.
- Free-tier limits: Verify which features are actually included at no cost. A test of a product does not by itself confirm what its free plan offers.
For context, AV-TEST says it evaluated 15 home-user security products in July and August 2026 using default settings and then-current public versions, scoring protection, performance, and usability at up to 6 points per category. Its Microsoft Defender Antivirus (Consumer) 4.18 report is specifically for Windows 11 Professional, English, 64-bit. These are results for that test cycle and setup—not a promise about another device, version, or future threat, and not proof that a system is infection-free.
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