can people steal your camera from the pack?

currently I use one of the Canon camera bags, its big its bulky and it gives me headaches and neckaches, so I was thking of buying one of those back pack type of bags thats has a compartment on teh back for camera and lensesm but I'm worried. Whats to keep some creep from unzipping the bag while walking behind me and taking the camera out? Has this ever happned to anyone? Again, I'm not talking aobut a regular backpack I'm talking about one of those made for cameras withe the compartment at the back.

check out the crumpler line, they have three backpacks that you have to take off to get the camera out. from smallest to largest they are the Keystone, Whickey and Cox, and the Karachi Outpost, I have the Karachi Outpost and it's awesome and there is no way anyone could get into the bag while it's on your back.

i dont think you should worry bout it. they are much more likely to "slice" your bag(cut the bottom out grab something and then run)
...just be aware of your surrounding and u should be ok
.............at least thats what the TV show i learned everything about my life said....
..oh yeh BTW minivans are cool again....my mom told me so

There are people that sell anti cut webbing for backpaacks and bags for travels in places like india where cut and grab is reasonably common.
http://www.pacsafe.com​/www/index.php

thanks for the ideas!