Does anyone know about IBIS "SIR" cases, what "SIR" stands for?

Does anyone know about IBIS "SIR" cases, what "SIR" stands for?

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Does anyone know about IBIS "SIR" cases, what "SIR" stands for?

Question 1: Does anyone know what "SIR" stands for?
and
Question 2: How does a naturalization application gets classified as a "SIR"?

http://judiciary.house.gov/media/pdfs/maxwell072706.pdf

On page 51, it talks about IBIS "SIR" Cases:

B. Instructions Regarding Pending IBIS “SIR” Cases Until further notice, no USCIS office is to perform resolution on any pending “SIR” Remember the “SIR” process terminated with the November 29, 2004 memorandum; all outstanding “SIRS” are now part of the backlog of “SIR” cases at the National Security and Threat Protection unit (NSTP—the component of ICE that assumed national security IBIS resolution activity from the INS National Security Unit). The ONLY National Security/Terrorism-related IBIS resolutions to be conducted by USCIS offices are thos eassociated with the National Security Notification (NSN) process created with the November 29, 2004 memorandum. When confronted with litigation, an office with a pending “SIR” should contact the FDNS for assistance. FDNS will request expedited processing from the NSTP for those cases ONLY