Security block for a communications connector

A security block for securing I/O ports of an electronic instrument physically prevents any breach of data through a protected I/O port, such as a USB port, by securing cables that may be plugged into the port by means of a locked cover. The cables are prevented from being removed and USB memory devices are prevented from being connected in their place. In a second aspect, a portion of the security block covers unused I/O ports thereby preventing USB memory devices and other devices from being connected to unoccupied I/O ports. The locking mechanism can be either a padlock, or a locking screw, or the like.