Intel is the general term for the secondary objectives that you can complete during the missions of the game. The difficulty setting determines the number of objectives that are required to be obtained otherwise you fail the mission. All of these intel objectives are supposed to be espionage like material that you pick. The titles are interesting and by picking them up, you unlock silver weapons for play later. Sorry, the weapons only look shiny, no special abilities.
There are 5 types of secondary objectives, but only 4 which are classified as "intel". These are Armament, Recon, Blackmail, and Intel. Armament is finding and picking up a hidden weapon during the mission. The Recon objective is a special looking objective that resembles a long, purplish tube, much like a container for a large map or poster. Both of these objectives can be found only once per level. Blackmail objectives are laptops, brief cases, or safes and always need to be shot or exploded in order to be picked up. Intel objectives are red file folders or small brief cases that contain pictures or information and can be located on walls, the ground, or on tables. These items are picked up running into them or walking over them.
The final type of secondary objective is destruction objectives, and these have their own guide and only are required on Black Ops mode.