AVG AntiVirus Free is a free and fairly comprehensive antivirus option when compared to paid options, and Panda Free Antivirus offers many of the same features. Windows 10 comes with free antivirus features as well through Windows Defender.
Windows Defender offers many of the same features as typical antivirus programs in its Windows 10 iteration. Because it's the default antivirus program, however, malware may seek to avoid it, so using a third-party tool can be prudent. Many antivirus programs also block malicious websites, and some scan websites users visit to look for signs of malicious activity. Of the free antivirus options available in 2015, AVG AntiVirus Free provides the most comprehensive tool kit, according to PC Magazine.