RE: How Secure is Windows, Really?

I've never relied on the screensaver to kick in as a way to protect the
PC.  For one thing, there's still a window, pardon the pun, of
opportunity between the time you leave and when the screensaver kicks
in.  Also, a modest vibration may move the mouse just enough for Windows
to think there's still activity going on.  Think someone the next cube
over slamming something on their desk or a feline at home playing
cat-n-mouse where the mouse happens to be from Microsoft or Logitech and
not from your basement.

Far safer is to manually lock the PC when you step away.  Ctrl-Alt-Del
followed by K will do it, although if your keyboard has the Windows key
(sometimes labeled as Start and having the Windows logo), Win-L is a
shortcut.

Personally I'd use a QT alternative or another media player altogether
instead of the Apple product.