Murray wants to know if he needs to install an antivirus for Windows 10. Leo says no. Windows 10 has its own antivirus that is automatically turned on called Windows Defender. But also, viruses spread so fast that antivirus software can't really keep up. It can't protect against 'zero day' exploits. Antivirus is really only a backup. The first line of defense is online behavior. The number 1 priority should be to keep the computer updated.