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For most Windows PCs, the first download you need is none. Windows 10 and Windows 11 include Windows Security, which runs Microsoft Defender Antivirus. Check that it is on and up to date before you install anything else. A separate free antivirus is worth downloading only if you want a different product, or if you need a cleanup tool for a computer you suspect is already infected.
Do you need a separate antivirus program?
Usually not. Microsoft documents Microsoft Defender Antivirus as part of Windows Security on Windows 10 and Windows 11, and it provides real-time protection once it is turned on. Installing a second antivirus is optional, and the reasons to do it are specific: you prefer another vendor’s interface, you want extra features such as a web protection extension, or you are cleaning up an infection that Defender has not caught.
The question “do I need antivirus if I have Windows Defender?” therefore has a practical answer. Defender is antivirus. What you may be missing depends on your habits and on the features you want, not on whether protection exists at all.
Recommended Free Tools
Check Windows Security first
Open the protection status before you search for a download. The steps below apply to Windows 11; on Windows 10 the same screen is reached through Settings, then Update & Security, then Windows Security.
#1 Best Overall
- THREAT DETECTION – Stay one step ahead. Suspicious links, risky sites, viruses, and scams, caught automatically before they reach you.
- PERSONAL INFO PROTECTION – Keep your personal info safer. Identity monitoring watches for your exposed info and tells you what to do about it.
- SECURE CONNECTIONS – Just a few easy clicks, and we'll automatically protect your info on public Wi‑Fi, every time you connect.
- GUIDED ACTION – Know what matters and what to do next. Clear alerts and simple guidance make it easy to take action.
- MORE THAN ANTIVIRUS – Scam protection, identity monitoring, VPN, web protection, and antivirus work together to protect you, all in one place.
- Click the Start button, type Windows Security, and press Enter.
- Select Virus & threat protection.
- Read the status message. A green check or a message stating that no action is needed means Defender is active.
- Select Virus & threat protection updates and then Check for updates to confirm that definitions are current.
- Confirm that Real-time protection is set to On under Virus & threat protection settings.
If any of these items shows a warning, fix it here first. Resolving a warning in Windows Security is usually faster than installing a new program on top of a misconfigured one.
What happens when you install another antivirus
Microsoft states that Defender Antivirus turns itself off when another antivirus app is installed and active, and turns back on after that app is uninstalled. This is why running two always-on antivirus products at the same time is not a sensible default. Two real-time scanners compete for the same files, which can slow the computer and produce false alarms, and the arrangement offers little extra protection in return.
Rank #2
![Norton 360 Deluxe 2027 Antivirus, 3 Devices, Auto-Renews [Download]](https://m.media-amazon.com/images/I/41qw3FS3qLL._SL160_.jpg)
- ONGOING PROTECTION Download instantly & install protection for 3 PCs, Macs, iOS or Android devices in minutes!
- TOP-PERFORMING VPN Faster speeds, more server locations, and greater connection control to protect your privacy across all your devices, including Smart TVs.
- ADVANCED SCAM PROTECTION Help spot hidden scams online. With the built-in Genie AI assistant, you’ll never wonder if a message or email is suspicious again.
- REAL-TIME PROTECTION Advanced security protects against existing and emerging malware threats, including ransomware and viruses, and it won’t slow down your device performance.
- DARK WEB MONITORING Identity thieves can buy or sell your information on websites and forums. We search the dark web and notify you should your information be found.
Plan the switch rather than layering products. Uninstall the old antivirus completely, restart the PC, and then confirm in Windows Security that Defender has returned before you rely on it.
Free options compared
These are the free options most readers encounter. The table records what each one is for and what the available sources establish. Free versions and their feature boundaries change, so confirm current details on the vendor’s official download page before installing.
Rank #3
- THREAT DETECTION – Stay one step ahead. Suspicious links, risky sites, viruses, and scams, caught automatically before they reach you.
- PERSONAL INFO PROTECTION – Keep your personal info safer. Identity monitoring watches for your exposed info and tells you what to do about it.
- SECURE CONNECTIONS – Just a few easy clicks, and we'll automatically protect your info on public Wi‑Fi, every time you connect.
- GUIDED ACTION – Know what matters and what to do next. Clear alerts and simple guidance make it easy to take action.
- MORE THAN ANTIVIRUS – Scam protection, identity monitoring, VPN, web protection, and antivirus work together to protect you, all in one place.
| Option | Best fit | What is established |
|---|---|---|
| Microsoft Defender Antivirus (Windows Security) | Readers who want built-in protection with no extra download | Included in Windows 10 and 11. Turns off automatically when another active antivirus is installed (Microsoft). |
| Avast Free Antivirus (within Avast One) | Readers who want a separate third-party product with real-time protection | Free tier provides real-time protection. Vendor lists 1 GB RAM, 2 GB disk space, and internet access for automatic updates. Vendor page lists Windows 11, 10, 8.1, 8, and 7 with edition exclusions. |
| Malwarebytes Free | Readers who suspect an infection and want a scan-and-clean tool | Vendor describes the free Windows version as scanning and cleaning malware. Ongoing real-time protection is described as a Premium feature. |
| AVG AntiVirus Free | Readers comparing free products on independent lab results | Included in AV-TEST’s August 2026 Windows 11 home-user test. Current download terms, feature boundaries, and requirements were not established from the sources reviewed. |
Avast Free Antivirus
Avast’s free antivirus is offered as part of Avast One. Its vendor page describes downloading the installer, opening it, approving the installation, and following the prompts. Automatic security and program updates require an internet connection, so an offline PC will not stay current. Avast also presents a paid upgrade path. Read the feature comparison on the download page before you assume the free tier covers everything you want.
Malwarebytes Free
Malwarebytes Free is best understood as an on-demand cleaner. It scans for malware and removes what it finds, which makes it useful when a computer is behaving strangely. It is not presented by the vendor as a substitute for always-on protection. If you want continuous real-time coverage from Malwarebytes, the vendor places that in its Premium product.
Rank #4
- SPEED-OPTIMIZED, CROSS-PLATFORM PROTECTION: World-class antivirus security and cyber protection for Windows (Windows 7 with Service Pack 1, Windows 8, Windows 8.1, Windows 10, and Windows 11), Mac OS (Yosemite 10.10 or later), iOS (11.2 or later), and Android (5.0 or later). Organize and keep your digital life safe from hackers
- SAFE ONLINE BANKING: A unique, dedicated browser secures your online transactions; Our Total Security product also includes 200MB per day of our new and improved Bitdefender VPN
- ADVANCED THREAT DEFENSE: Real-Time Data Protection, Multi-Layer Malware and Ransomware Protection, Social Network Protection, Game/Movie/Work Modes, Microphone Monitor, Webcam Protection, Anti-Tracker, Phishing, Fraud, and Spam Protection, File Shredder, Parental Controls, and more
- ECO-FRIENDLY PACKAGING: Your product-specific code is printed on a card and shipped inside a protective cardboard sleeve. Simply open packaging and scratch off security ink on the card to reveal your activation code. No more bulky box or hard-to-recycle discs. PLEASE NOTE: Product packaging may vary from the images shown, however the product is the same.
AVG AntiVirus Free
AVG AntiVirus Free posted the same protection, performance, and usability results as Avast Free in AV-TEST’s August 2026 test, described below. That result tells you how the product scored in one lab test. It does not tell you the current download terms or whether the free edition will show upgrade prompts, so check the official page at the time you download.
What the independent test results show
Two independent test series are relevant here, and they differ in age and scope.
Best Value
![Norton 360 Deluxe 2027 Antivirus, 5 Devices, Auto-Renews [Download]](https://m.media-amazon.com/images/I/41IYV5zGyCL._SL160_.jpg)
- ONGOING PROTECTION Download instantly & install protection for 5 PCs, Macs, iOS or Android devices in minutes!
- TOP-PERFORMING VPN Faster speeds, more server locations, and greater connection control to protect your privacy across all your devices, including Smart TVs.
- ADVANCED SCAM PROTECTION Help spot hidden scams online. With the built-in Genie AI assistant, you’ll never wonder if a message or email is suspicious again.
- REAL-TIME PROTECTION Advanced security protects against existing and emerging malware threats, including ransomware and viruses, and it won’t slow down your device performance.
- DARK WEB MONITORING Identity thieves can buy or sell your information on websites and forums. We search the dark web and notify you should your information be found.
- AV-TEST, August 2026, Windows 11 home-user evaluation: Avast Free Antivirus 26.6 scored 6 out of 6 for protection, 6 for performance, and 6 for usability. AVG Antivirus Free 26.6 and 26.7 scored the same. Microsoft Defender Antivirus (Consumer) 4.18 scored 6 for protection, 5.5 for performance, and 6 for usability. Each category had a maximum of six points. These scores apply to the listed versions, in AV-TEST’s Windows 11 environment, and do not guarantee the same results on every PC or in later versions.
- AV-Comparatives, September 2025 Malware Protection Test: The test assembled 9,995 malware samples and ran on an up-to-date 64-bit Windows 11 system. It included Avast Free Antivirus 25.8, AVG Antivirus Free 25.8, and Microsoft Defender Antivirus 4.18. Because it is a year older than the AV-TEST result, treat it as background on method rather than the latest ranking.
AV-Comparatives itself advises readers to consult other recent reports and to weigh price, ease of use, compatibility, and support. Read one test as one data point. Neither series shows that any product is universally the best choice.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to download safely
- Start from Windows Security, as described above. If it is active and current, you may not need a download.
- Go directly to the vendor’s own website. Do not use download aggregators or links in pop-up advertisements.
- Confirm the exact product name, such as Avast Free Antivirus or AVG AntiVirus Free, and compare it with the name on the page you reached from the vendor’s home site.
- Check the operating system and hardware requirements on the vendor page. Requirements can change between releases.
- Run the installer, approve the prompts, and restart the PC when asked.
- Open the product and confirm that real-time protection and automatic updates are enabled. Then check Windows Security again to confirm that Defender has switched off as expected.
If you suspect an infection
Symptoms that justify a cleanup scan include unexpected pop-ups, a browser that redirects to unfamiliar sites, programs that install without your action, and a sudden drop in performance with no obvious cause. Treat these as reasons to scan, not as proof of infection.
- Run a full scan with Windows Security (Virus & threat protection, then Scan options, then Full scan) before installing a second tool.
- If you want a second opinion, use an on-demand cleanup tool such as Malwarebytes Free, which is designed for scanning and removal.
- Do not leave two real-time antivirus products running together afterward. Keep one always-on product and use the other only for scans, and remove the cleanup tool once the scan is complete if your main protection is already in place.
- Change passwords for important accounts from a clean device if you entered credentials on the suspected PC.
Limits of this guidance
This guide covers Windows PCs. Microsoft’s built-in coverage applies to Windows 10 and Windows 11. Avast’s page lists older Windows versions as compatible, but compatibility does not mean those systems still receive security updates from Microsoft or any other vendor, so an older PC is a reason to upgrade the operating system rather than rely on a third-party product alone. The sources reviewed do not provide a complete feature-by-feature comparison of every free antivirus product, and product terms change, so confirm details at the vendor site before you download.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
When you are unsure which option fits, start with Windows Security, keep it updated, and add a third-party tool only for a specific reason you can name.
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