Avast Antivirus is a family of internet security applications developed by Avast for Microsoft Windows, macOS, Android and iOS. The Avast Antivirus products include free and proprietary versions that provide computer security, browser security, antivirus software, firewall, anti-phishing, antispyware, and anti-spam among other services.As of 2017, Avast is the most popular antivirus on the market, and it had the largest share of the market for antivirus applications.