I run the (stock) Microsoft Windows Defender on 2 LTs and one DT (all W10 and dual boot). I haven't had any issues. YMMV. On my wifes LT(personal for real estate) I also run Norton AV as she is not as paranoid as I am and tends to click URLS a lot. I occasionally run Malwarebytes on it if I think there is an issue. john mitchell