According to a report yesterday from the Washington Post, the National Security Agency (NSA) has constructed a surveillance system that is capable of recording the entirety of a foreign country’s phone calls. The agency is then capable of reviewing the contents of the calls for as long as a month after the collection of the information. This information is another in the series of disclosures from Edward Snowden.

According to the National Journal, the NSA’s program includes the contents of Americans’ phone conversations. In a statement to the National Journal, a spokesperson for the NSA said that it “does not conduct signals intelligence collection in any country, or anywhere in the world, unless it is necessary to advance U.S. national security and foreign policy interests.”

The NSA’s tool is named named RETRO. RETRO is short for retrospective retrieval. RETRO is a tool under the MYSTIC program, which began in 2009. According to the report, the program keeps a rolling, 30-day inventory. When a call is older than 30 days, it it removed from the database.

Citing until-now-unpublished documents, the Post explains that RETRO allows the NSA to query 100 percent of a foreign country’s calls, even if the original target was “not tasked at the time of the original call.” This means that someone who was not the target of an investigation could have their calls collected and later, once becoming the target of an investigation, have calls reproduced from before they were a target.

According to government officials this type of spying is not an unnecessary intrusion into the sovereignty or privacy of individuals. Instead, it’s merely a means of bulk collection and the majority of the data is never even used. It raises concerns, though, that a program like RETRO can, in a moment, turn what was practically anonymous data into a focused and targeted part of an investigation.

Joshua is a writer and researcher with Ring of Fire. You can follow him on Twitter @Joshual33.