How to Prevent IP Theft by Your Own Employees?

Cursed by USB asks: "We are a small software startup based in India. Recently one of our employees was caught trying to steal our IP (work) from a computer using a USB thumb drive. While all the staff computers are devoid of floppy drives, cd writers and internet connections, we simply cannot disable the USB ports since there are a lot of USB enabled peripherals that we use. Apart from trying to hire "trustworthy" people, are there any other bright ideas that Slashdot readers might have in this regard to help prevent such theft from workplace?"