Imperial Security Bureau Stormtrooper

Imperial Security Bureau Stormtroopers, or ISB Troopers for short, are similiar to regular Stormtroopers in almost all respects with just a few key differences. The most important is that although ISB Troopers are technically considered to be a part of the Stormtrooper Corps, they operate outside of Stormtrooper Command and only take orders from the Imperial Security Bureau. As they wear identical armor to that of regular stormtroopers, they are sometimes used to infiltrate standard units of stormtroopers to ensure their loyalty and the execution of their orders.

In fact it can be said that ISB Troopers are even more fanatical to the New Order than the standard stormtrooper. Somewhat paradoxically, ISB Troopers are also known to find ways to interpret their orders that allow them to take extra measures to ensure the safety and stability of the Empire, up to and including the elimination of any perceived disloyal member of the Empire.

=Sources=
 * Wookieepedia