Using a usb webcam as a standalone cctv system.

Hey i am new to Arduino and i wondered if theres someway to use an arduino with a sd shield to record an usb video signal to make a cheap, small and unhackable standalone surveillance system that can be mounted in a wall for example to make it hidden

I'm not sure what 'unhackable' means in this context. An Arduino isn't a suitable platform for recording video, but there are plenty of small video cameras with SD storage capability and I'm sure that there is already a big market in "spy cameras" that would probably meet your requirements.