GiliSoft USB Lock is a comprehensive tool which tries to prevent confidential files being copied from your PC.
The program can prevent users writing to USB disks, or burning CDs/ DVDs, as well as disabling SD Card Readers and blocking connections to Android and iPhone devices.
If that sounds too inflexible, you're able to create a whitelist of your own devices. These will work correctly, while everything else gets blocked.
There are other ways to transfer data, of course, but GiliSoft USB Lock can block most of those with a click: printers, modems, COM/ LPT, infrared, Bluetooth, Firewire/ 1394.
If the user can get online, you're still in trouble. Fortunately, you're able to restrict web access to specific websites only, or even disable network adapters.
A determined hacker might try to remove GiliSoft USB Lock's protection, but that's not going to be easy. The program is password-protected, and you're able to disable Task Manager, REGEDIT, Remote Desktop Connection, and block specific programs from running.
Please note, the trial version only works for the first 10 minutes after launch. If that's not enough, restart and it'll work again. Buy the product and all restrictions are removed.
GiliSoft USB Lock does a good all-round job of locking down your PC, but the possible restrictions (no, or extremely limited internet access) may be a problem for some.