Security. so those are the three levels of classification. within those three levels there are compartments of segmentation of specific types of information which are restricted for the most part on a need to know basis. so just because somebody has a top secret clearance does not necessarily mean they have access to everything that's top secret. within that layer, particularly secret and top secret, there are categories, sub categories, compartments or what are called special access programs. sci, special compartmented information includes, for example, signals intelligence. the lion's share ...