30 years of experience with hundreds of millions of users help to make Avast continue to have the best free antivirus for your PC. We use 6 layers of security: 1. Web Shield - scans for phishing sites and risky malware whenever you're online. 2. File Rep - compares files against known malware in our giant, and constantly updated threat database. 3. Emulator - we pretend to be your computer and run files to test them. 4. DeepScreen - we check to see if the file acts even remotely similar to known