From AVG Technologies:
AVG Free Edition is the well-known antivirus protection tool. AVG Free is available free of charge to home users for the life of the product. Rapid virus database updates are available for the lifetime of the product, thereby providing the high level of detection capability that millions of users around the world trusts to protect their computers.
AVG Free is easy to use and will not slow your system down (low system resource requirements. Highlights include automatic update functionality, the AVG Resident Shield, which provides real-time protection as files are opened and programs are run, free Virus Database Updates for the lifetime of the product, and AVG Virus Vault for safe handling of infected files.
Version 7.5.516 features improvements in Resident Shield scanning and adds small improvements in installation process. Download