The most popular antivirus programs for Windows computers are Microsoft Security Essentials, avast! Free Antivirus and Avira Free Antivirus, as of 2015. The market share for Microsoft Security Essentials leads at 17.8 percent of Windows computers, followed by avast! Free Antivirus at 17.6 percent. This number drops to 5.9 percent for Avira Free Antivirus. While these are the most installed antivirus programs, Windows 8 and above comes preinstalled with Windows Defender, an antivirus program that replaces Microsoft Security Essentials.
Microsoft Security Essentials is an antivirus program for Windows 7 and Vista. This program offers real-time protection with both online and offline virus scanning and removal. This antivirus identifies viruses using its dynamic signature service. Windows Defender improves upon Microsoft Security Essentials with enhanced rootkit and bootkit protection.
Avast! Free Antivirus offers intelligent virus and malware protection, scans home networks for security flaws, and cleans up unwanted browser add-ons. In addition to the free version, avast! also sells its antivirus with additional features.
Avira Free Antivirus provides real-time protection from all types of viruses. The program secures the data of computers and protects privacy by blocking ad networks from watching users. The antivirus also features cloud technology that compares the digital fingerprint of suspicious files against Avira's online database.