Beware high dense bushes blocking your view of anyone hiding near a window or door. They are a security risk because someone can hide behind them and either break in or attack you from hiding.  If you have them be sure to trim them down below 4 feet.

On the other hand, the right kind of thorny bush can be a wonderful deterrent.  Really strong, thorny bushes planted under windows and next too doors can prevent people from getting too close.  Check with a local arborist or garden center for the plants that will thrive in your area but be sure you get really thorny ones.  If you tell the garden center or arborist why you want these bushes (for security purposes) a good one will know what you need.

BTW:  you can use these same plants in other ways and places too–like near gates in your fence or next to your garage door.