I just wanna point out Windows Defender DOES have online protection, and it's gotten in my way pretty frequently. Whenever a new steam game is released it interferes with the download (goes from nearly a Gb/s to zero) while it scans the files being downloaded. And then when you start the game up loading times are in the 10 minute+ range because it's analyzing the binary.

You can disable these features though by turning off real time protection (which I had to do).