Foremost, only Windows Defender comes installed with Windows so you have a couple of options like I mentioned instead of using Defender if you feel uncomfortable trusting Windows products. Though for the sake of argument, I must mention here that most support products like Defender, Security Essentials, Firewall etc were designed by think tanks not affiliated with Windows initially but later absorbed into it instead of writing a bunch of protective programs from scratch. A comparable example that Microsoft is known for doing something like that would be the buyouts of known tech projects like Skype, Hotmail and recently Nokia. So as far as the quality of these pre existing softwares, renamed under Windows flagship, goes I personally feel they are up there and at least close to equal if not better compared to it's competitors. Even, when most anti-viruses go nuts tagging harmless cracks as viruses, Windows support softwares seldom would ever give me false positive and I dabble in a lot of "not-so-original" games.