The Best Free Antivirus in 2025 — Tested, Not Guessed

First: The Honest Case for Windows Defender

Windows Defender — officially called Microsoft Defender Antivirus — is free, built into Windows 10 and 11, never nags you to upgrade, and doesn't harvest your browsing data to sell to advertisers. In 2019 it was mediocre. In 2025, it's genuinely good. AV-Test rates it in the "top product" category consistently. False positives are low. Performance impact is minimal because Microsoft has had years to optimise its integration with the OS.

For the average Windows user with sensible browsing habits, up-to-date Windows, and a password manager, Microsoft Defender is sufficient. There. I said it. A lot of sites won't because they earn commission every time you click a "free" antivirus link that leads to a freemium upsell funnel.

That said, two free third-party options outperform Defender in specific areas, and they're worth knowing about.

Bitdefender Free Edition

Bitdefender's free tier uses the same detection engine as the paid versions. That's significant — the underlying technology is excellent. In my testing, it matched or exceeded Defender's detection rates and had fewer false positives. What you don't get is real-time ransomware protection, a firewall, VPN, or any of the extras from the paid suite. But the core malware detection is strong.

The catch is the interface: the free version exists mainly to get you into the Bitdefender ecosystem and encourage an upgrade. It shows you what features you're missing. That's reasonable honestly — they're not hiding it. But it means living with a dashboard that has a lot of greyed-out options. If that doesn't bother you, the protection quality is among the best available at any price.

Malwarebytes Free

The free version of Malwarebytes is a scanner, not a real-time protector. You have to run it manually. This makes it useless as a primary security product — but invaluable as a second opinion or cleanup tool. If you have an infection suspicion or you've just bought a secondhand laptop and want a clean sweep, Malwarebytes Free is what I reach for before anything else. Keep it installed alongside Defender.

What to Avoid

Several free antivirus products are genuinely worse than having nothing, not because their detection is poor, but because of what they do with your data. Avast Free and AVG Free (the same company under different branding) have a documented history of selling user browsing data to third parties. A security product that monetises your data is a strange kind of security. Both are still widely recommended because affiliate commissions are generous. We don't recommend them.

Similarly, several free products are genuinely free versions of paid tools with such aggressive upselling built in — popups, desktop notifications, browser homepage hijacking — that the experience is worse than the protection is worth.

Our Recommendation

For most people: use Windows Defender and don't overthink it. Keep Malwarebytes Free installed and run it manually every couple of months or whenever something feels off. If you want genuinely better detection than Defender without paying, Bitdefender Free Edition is the upgrade. If you have the budget, Bitdefender Total Security paid is the one we'd actually recommend spending money on — the gap between it and free alternatives is noticeable in our testing.