New secret documents published online today lay out the ground rules for the shadowy National Security Agency when it comes to "inadvertently" spying on Americans, showing the U.S. government can use information it accidentally collects about its own citizens without a warrant.

Published by the U.K. newspaper The Guardian, a pair of documents reportedly filed to the super secret Foreign Intelligence Surveillance Act court spell out first the steps the NSA takes to avoid spying on its own citizens individually - extensive protocols it calls "minimization" - and then what the agency must do with the information it may get anyway. The documents are both stamped 2009 and one shows the signature of Attorney General Eric Holder.

The NSA is allowed to target and spy on non-American individuals who are outside the U.S., but the methods by which the NSA determines someone's "foreignness" are hardly an exact science. As the documents show, during its "minimization procedures," NSA analysts look at a number of factors, including information from the communications themselves, information about the device used to communicate or publicly available information, until they have a "reasonable belief" one way or the other about the person's location and citizenship.

One quick way to find out, according to the documents, is for the NSA to check the phone number or email address of the potential target against a database the agency keeps containing information on known American phone and electronic communication information "in order to prevent the inadvertent targeting of a United States person." If the numbers or addresses match, the person cannot be spied on under current circumstances, the documents say.

If the NSA analysts still cannot tell if the person is a U.S. citizen or is inside the country, the person is "presumed to be a non-United States person" unless new information indicates otherwise.

DOCUMENTS: NSA Minimization Procedures | Procedures to Target Non-U.S. Persons (The Guardian)

If a target of the surveillance is later found to be inside the U.S., the NSA is required to stop spying on them immediately. But as the documents show, the information the agency has already collected on the now-illegitimate target doesn't necessarily disappear.

The documents say the acquired communications will not be destroyed if there is a "reasonable belief" they contain "significant foreign intelligence information," "evidence of a crime," or are encrypted or pose a "threat of serious harm to life or property."

ABC News was unable to independently verify the documents and spokespersons for the FBI and the Department of Justice declined to comment. Previously, DOJ and FBI officials have said they are not allowed to view leaked secret documents, even if they are posted publicly online, if the officials are not directly involved in a related investigation.

The Guardian report is the most recent in a string of stories revealing the inner workings of the NSA, formerly nicknamed "No Such Agency." Though his name does not appear in The Guardian's report today concerning the secret documents, previously the newspaper's scoops allegedly have been based on information provided by Edward Snowden, a former NSA contractor who fled to Hong Kong before revealing his old employer's secrets. Snowden confessed to being the leaker in a previous interview with The Guardian, calling the NSA's surveillance programs "horrifying."

The first in the series of stories concerned a secret FISA document that compelled Verizon to hand over records of millions of is customers in the U.S. - part of a separate NSA program that U.S. officials maintain is not individualized targeting. At the time, it was a mystery to U.S. law enforcement officials as to how Snowden had access to the closely held FISA documents while working as a systems manager with the NSA, prompting fears he may have been working with another person.

Earlier this week the head of the NSA, Gen. Keith Alexander, solved the mystery when, shortly after a congressional committee hearing, he told reporters that Snowden accessed a classified web server containing the FISA document as he was undergoing specialized network training.

TIMELINE: Edward Snowden's Life as We Know It

Today it was also revealed during a congressional hearing that USIS, the contracting firm that conducted a background check for Snowden, a 29-year-old high school drop out, has been under investigation for two years by the Inspector General for the Office of Personnel Management for apparently failing to adequately conduct investigations. The IG for OPM also told a congressional panel today that there may have been problems in the way that USIS conducted Snowden's background check in 2011.

In order to get a security clearance to access classified information federal employees and contractors must first clear background checks and over 90 percent of the background checks are conducted by OPM. USIS is one of the three major contractors that conducts background checks for the U.S. government and conducts 45 percent of the overall contract workload. The company received $200 million in federal contracts last year.

ABC News' Luis Martinez and James Gordon Meek contributed to this report.