Uninstall Windows Defender (Vista Ultimate)

I am running Windows Vista Ultimate and Microsoft Defender is installed by
default. I want to uninstall it but it doesn't even show up in the Programs &
Features list (Uninstall or change a program). How do I go about to uninstall
that program.

thank you

Hello,
Windows Defender ( not microsoft defender, by the way) is part of Vista. It canNOT be un-installed. You can, however, turn it off.
BUT, before you turn it off, do you have a 3rd party program to replace it ? You must have one or the other. Assuming that you do, open windows defender, look to the top, find the ( ? ) sign, click it . Perhaps you want to read what's on the screen first. Scroll all the way to the end, click the last entry : Turn windows defender on or off. Just follow the instructions on how to turn it off.