I have set up my Win 7 Pro 64-bit screen saver to bring up the password logon screen upon activation of the mouse/keyboard/whatever.
Late last week, whenever I moved the mouse or clicked the keyboard, the screensaver would go directly to the desktop, bypassing the logon screen. I went to the screensaver utility and unchecked and rechecked the 'On resume, display the logon screen' box, selecting 'Apply and OK' each time.
This would work for maybe two or three times and then go back to returning to the desktop.
I've run MalwareBytes, IOBit, and Norton and all come up virus/rootkit free.