Four free antivirus options dominate most recommendation lists. Three are worth using. One sold your browsing data to data brokers for years before getting caught. What each tool does, what it skips, and which one to run on your computer today.
Windows Defender: The Default That Earned Its Spot
Windows Defender (now called Microsoft Defender Antivirus) ships with every copy of Windows 10 and 11. AV-TEST, the independent antivirus testing lab, gave Defender a 6.0/6.0 protection score in its June 2026 consumer product evaluation. That score ties it with Kaspersky, Bitdefender Premium, and Norton 360.
Defender activates automatically, updates through Windows Update, and runs real-time protection in the background without any configuration. For users who want something that works without thinking about it, Defender is the honest answer. The only scenarios where you need to supplement it: you download software from sketchy sources frequently, or you need ransomware file rollback (Defender does not recover files that ransomware has encrypted — that feature requires Microsoft 365 Personal or higher).
One important note: Defender backs off automatically when you install a third-party antivirus. If you later uninstall that third-party tool, verify Defender has re-enabled itself in Windows Security settings.
Malwarebytes Free: On-Demand Only — Read This Before Installing
Malwarebytes Free is widely recommended, but most articles bury the critical limitation. When you install Malwarebytes, it starts a 14-day trial of Malwarebytes Premium with full real-time protection. When the trial ends, real-time protection deactivates. The software does not warn you loudly. The icon stays in your taskbar. Your computer looks protected but is not.
In free mode, Malwarebytes is an on-demand scanner — you open it manually, click Scan, and it checks your system for existing malware. It does not monitor downloads, block malicious websites, or intercept threats as they arrive.
The right way to use it: keep Windows Defender active for real-time protection, install Malwarebytes Free as a second-opinion scanner, run manual scans weekly. This combination costs nothing and provides both passive and on-demand coverage without conflicts.
Bitdefender Antivirus Free: Real-Time Protection, Windows Only
Bitdefender Free Edition provides genuine real-time protection with no nag screens and no data selling. It consistently scores 6.0/6.0 in AV-TEST protection evaluations, the same as Bitdefender's paid tiers for signature-based malware detection.
The honest limitations: Windows only (no Mac or Android version in the free tier), no firewall (relies on Windows Firewall), no VPN, no phishing protection for email clients. If you want a second real-time scanner beyond Defender, Bitdefender Free is the cleanest option available. Do not run it alongside Defender's real-time protection simultaneously — one will need to be your primary scanner.
Mac users: Bitdefender does offer a free Mac scanner, but it is a manual on-demand tool, not continuous protection. macOS includes its own XProtect malware scanning built into the OS.
Avast Free Antivirus: The Data Selling Scandal You Should Know
Avast was the world's most installed free antivirus for years. In January 2020, Motherboard and PCMag published an investigation revealing that Avast collected detailed browsing data through its browser extension and sold it via a subsidiary called Jumpshot. The data included search queries, product page visits, and YouTube watch history — linked to device identifiers, not anonymized at the individual level despite Avast's claims.
Avast shut down Jumpshot in January 2020 under public pressure. In February 2024, the FTC settled with Avast, requiring a $16.5 million payment and prohibiting Avast from selling or licensing browsing data for advertising. The FTC specifically cited the gap between Avast's privacy promises and its actual data practices.
Avast's antivirus detection scores remain competitive. The question is whether a company with this specific history should be trusted with software that has deep system access and browses your network traffic. Alternatives with equivalent detection rates and no comparable history exist: Windows Defender and Bitdefender Free are both options.
AVG, which Avast acquired in 2016, shares the same infrastructure and ownership. The same caution applies.
What Free Antivirus Cannot Do
Every free antivirus tool has the same set of gaps. Know them before you decide you're fully protected:
Ransomware rollback. Free tools detect ransomware and can prevent it from running. If ransomware encrypts your files before detection, no free antivirus recovers them. File backups (external drive, cloud backup) are the only reliable recovery method. Windows' built-in Backup and Restore or a service like Backblaze covers this.
VPN. Free antivirus does not encrypt your internet connection. Your ISP still sees your traffic. On public Wi-Fi, your connection is unencrypted at the network level regardless of antivirus. A separate VPN is required for that protection — see our free trials page for VPN trial options.
Identity monitoring. Free antivirus does not alert you when your credentials appear in breach databases. You can check this manually for free at haveibeenpwned.com, or set up free breach alerts to monitor your email addresses automatically.
Technical support. Free tiers receive no phone or chat support. Community forums and documentation only.
The Honest Recommendation
For most Windows users: Windows Defender alone is sufficient for everyday protection. Add Malwarebytes Free for manual weekly scans. Enable Controlled Folder Access in Windows Security settings to add ransomware protection to Defender (it prevents unknown applications from modifying your Documents and Desktop folders).
If you want Defender replaced rather than supplemented: Bitdefender Free Edition has no data controversies and equivalent detection scores. Install it, let it disable Defender automatically, configure nothing else.
Skip Avast unless you have read the FTC settlement and decided the post-2020 policy changes satisfy you. The detection scores are not meaningfully better than alternatives without the same history.
Frequently Asked Questions
Does Windows 11 need a separate antivirus?
For most home users, no. Microsoft Defender Antivirus is built into Windows 10 and 11 and scores 6.0/6.0 in AV-TEST lab testing — the same score as paid competitors like Kaspersky and Bitdefender Premium. It runs real-time protection silently in the background, updates automatically through Windows Update, and costs nothing extra. The main gap is ransomware rollback (Defender does not recover encrypted files) and identity monitoring, which require paid upgrades.
Does Malwarebytes Free protect my computer in real time?
No. Malwarebytes Free is an on-demand scanner only. After the 14-day Premium trial expires, real-time protection turns off silently. Many users do not notice. You must manually open the app and run a scan to check for threats. For passive background protection, pair it with Windows Defender (which stays active) and run Malwarebytes scans weekly or after suspicious activity.
Is Avast still safe to use after the 2020 data scandal?
Avast sold detailed browsing data through a subsidiary called Jumpshot from 2019 to early 2020. The data included search queries and site visits linked to device identifiers, even from users who had not opted into data sharing. The FTC and FTC reached a settlement in 2024 requiring Avast to pay $16.5 million and prohibiting it from selling browsing data going forward. Whether that policy change is trustworthy is a judgment call. Less-risky alternatives exist.
What does free antivirus not protect against?
Most free antivirus tools lack: ransomware file rollback (recovering encrypted files requires paid tiers), VPN access, identity theft monitoring, dark web scanning for your personal data, phishing protection in email clients, and technical support. Free tools detect and remove known malware well. The gaps are in recovery, monitoring, and proactive threat intelligence.
Can I run two antivirus programs at the same time?
Not two real-time antivirus programs simultaneously — they conflict, flag each other, and degrade performance. The safe combination is one real-time scanner (Windows Defender or Bitdefender Free) plus one on-demand scanner run manually (Malwarebytes Free). This covers both passive protection and periodic deep scans without conflicts.