A security system with methodology for defending against security breaches of peripheral devices is described. In one embodiment, for example, a method is described for protecting a computer from security breaches involving devices that may be attached to the computer, the method comprises steps of: when a device is first attached to the computer, specifying authorization information indicating that the device is allowed to communicate with the computer; detecting detachment of the device from the computer; updating the authorization information to indicate that the device is no longer authorized to communicate with the computer; and upon reattachment of the device, blocking communication with the device while the device remains unauthorized, thereby preventing a security breach involving the device.