How do I make the 'X' default button on a form either invisible or disabled

I have a windows SignIn form in my c# application (see below)

I want to ensure that users only exit this form by using the exit

button created by me and NOT  the default 'X'.

How do i make the 'X' button in red above either invisible or disabled

on this form.

The minimize and maximize button should be left as is.

Thanks