Avast One

Protect your Windows 8.1 PC with our free antivirus

Your Windows 8.1 PC deserves an antivirus trusted by hundreds of millions of users worldwide.

Get your Windows 8.1 PC running smoothly

We’re more than just free antivirus. Avast also protects your Windows 8.1 PC’s performance, using cloud-based processing to secure you without slowing you down. In addition, you can optimize Windows 8.1 with Avast Cleanup available in the Avast One app, which will adjust settings, clear junk data, and clean out your registry to get your Windows 8.1 PC running as good as new.

Essential antivirus protection for Windows 8.1

Avast One with Free Antivirus delivers strong protection against zero day malware threats on Windows 8.1. Combined with advanced privacy and security features like VPN, it helps keep you and your PC protected from evolving online threats.

Microsoft-approved security for Windows 8.1

Avast is one of Microsoft's official consumer security software providers – ensuring our place as one of the most beloved, trusted antiviruses on the net, used by hundreds of millions of users around the globe.

We’re award-winning by nature, not just by name

We can help protect you against advanced online threats, backed by one of the world’s largest consumer Cyber Safety networks. And we’ve been proud winners of different awards over the years. Check out some of our more recent ones below. The award-winning protection from Avast Free Antivirus is also available in the Avast One app.

2025

“95% phishing-page detection rate, no false alarms”

AV-Comparatives
Anti-Phishing Comparative Test

 

2025

“100% real-world threat samples detected and blocked”

AV Test
Home User Protection Test


 

2025

“Total Accuracy Rating: 100%, False Positives: 0%”

SE Labs 
Security Evaluation Test: Home Anti-Malware

2025

“95% phishing-page detection rate, no false alarms”

AV-Comparatives
Anti-Phishing Comparative Test

2025

“100% real-world threat samples detected and blocked”

AV Test
Home User Protection Test

2025

“Total Accuracy Rating: 100%, False Positives: 0%”

SE Labs 
Security Evaluation Test: Home Anti-Malware

You may still be wondering...

FAQs

Every PC needs protection and Windows 8.1 PCs are no exception. Windows 8.1 does have built-in security software, however, it is widely accepted that this built-in security is not enough. Therefore for better online security, you need a third-party antivirus to keep you safe from viruses, ransomware, and other malware.

Windows 8.1 does have Windows Defender built-in, however, it only offers basic protection to Windows 8.1 PCs. Therefore, for true online security, it would benefit you and your device to invest in third-party antivirus software that can make up for the limitations of Windows Defender.

Yes. Windows Defender is free, as it comes built-into Windows 8.1. However, if you’re looking for more comprehensive security software, Avast offers a free antivirus for Windows 8.1. The free version of Avast antivirus for Windows 8.1 provides powerful and comprehensive protection that should more than suffice for your needs. If you would like more security, however, you can also download a 30-day free trial of Premium Security in the Avast One app.

Avast One with Free Antivirus for Windows is one of the best Windows antiviruses by far due to our powerful security and additional features. We use six layers of security to ensure you have protection from 0-day threats. Additionally, our automatic spyware removal tool can keep your data private, and we make removing viruses already on your Windows 8.1 PC easy. Best of all, we’re absolutely free, so you can download and install our protection without paying anything.

Visit our Support Center for more FAQs