Another one of the Bond Easter Eggs. This time MGM have supplied some information on SPECTRE on the disc.
From the main menu, select the “Special Features” entry, and then press the left arrow key on your remote control. This will highlight the “Spectre” logo, and pressing “Enter” will take you to the hidden section.

Note: This hidden feature can only be found on the original DVD release of this film and is not part of the re-released Special Edition.