Have you ever wondered why Linux systems seem to get hacked so much less than Windows? Here is an excellent example:
Imagine for a moment someone at a Windows conference going on for an hour, with source code and subsystem examples, all the ways he could imagine hacking into Windows via the USB system.
Well, no, can't do that because Microsoft does not allow anyone who has access to the source code and subsystems in Windows to do such presentations. Any such exploits can only be hypothetical, and really smart people who do not work for Microsoft cannot make changes to that source code and submit them to Microsoft.
All that is not just possible in the UNIX, Linux and BSD environments, it's encouraged!
That said, complacency is the greatest danger to computer security. Just because you run Linux does not mean you can run every binary and script someone sends to you. ...and get away with it forever!