Privacy advocates expressed interest Tuesday in curtailing "backdoor searches" of U.S. Internet records, while other policy experts and lawmakers said "U.S. person queries" aren't cause for concern.

The two terms – one alarming, the other dull legalese – both describe a practice that took center stage at the Senate Judiciary Committee's kickoff hearing about whether to modify a 2008 surveillance package that expires at the end of next year.

A part of that law – known as Section 702, an amendment to the Foreign Intelligence Surveillance Act – allows the National Security Agency to acquire without a warrant the communications of foreigners living abroad.

There are two major collection programs authorized under Section 702. The PRISM program takes records directly from major companies like Facebook and Google, while "upstream" collection siphons communications related to a "selection term" from the cables and switches that make up the Internet's backbone.

An unknown number of Section 702 intercepts involve domestic communications or innocuous ones between an American and someone abroad. Once collected, intelligence agencies are free to search the records tied or belonging to Americans, even in ordinary criminal investigations.

The term "backdoor search" – when applied to this practice, as it was during Tuesday's hearing – implies an improper side-stepping of Fourth Amendment protections. But defenders of the status quo see nothing wrong with reusing what they and some courts consider lawfully collected intelligence.

"Whoa, whoa, whoa, what do you call – what's a 'backdoor search'?" asked Sen. Dianne Feinstein, interrupting Elizabeth Goitein of New York University's Brennan Center for Justice.

Feinstein, a California Democrat and former chairwoman of the Senate intelligence committee, undoubtedly was familiar with both the term and the practice, which the House of Representatives twice has voted to prevent. The approved House amendments, which eventually were dumped from deals negotiated by congressional leaders, also sought to forbid government-mandated technology flaws that enable surveillance.

"A backdoor search is when the FBI or any other agency targets a U.S. person for a search of data that was collected under Section 702, which is supposed to be targeted against foreigners overseas," Goitein told Feinstein. "The FBI gets raw data, the NSA and CIA get raw data, and they search that raw data using U.S. person identifiers."

"That's what I call backdoor searches," she said, adding with apparent amusement, "I'm happy to call it 'U.S. person queries.'"

The intelligence community has not provided an estimate of the number of Americans whose records are collected under Section 702, despite inquiries from lawmakers. There's slightly more claritiy on the number of searches performed, however.

A report issued last month by the Office of the Director of National Intelligence said there were 23,800 queries in 2015 concerning known U.S. persons. But the domestic law enforcement-focused FBI did not provide a number, saying it does not track that data.

Rachel Brand, a member of the presidentially appointed Privacy and Civil Liberties Oversight Board, said at the hearing there's much concern about nothing. The FBI, she said, does not use the voluminous "upstream" intercepts, which can net a communication merely if the body of an email contains a keyword.

And "the NSA targets only a tiny fraction of a percentage point of Internet users in the world," she said. "It's extremely unlikely that 702 information is ever going to come back in a regular criminal investigation."

Brand said the FBI doesn't track the number of queries it performs because the information is contained in a database that contains other records, which can be searched as a preliminary step in investigations.

Meanwhile, at the CIA and NSA, "there are extensive rules and protections that surround the use of U.S. person queries. ... What Ms. Goitein refers to as a 'backdoor search,'" Brand said. At the FBI, she said, "the protection comes in the use of the information," as the FBI is supposed to disclose its origin in legal proceedings.

Brand said she doesn't believe lawmakers should craft legislative changes to Section 702, though she does support administrative efforts to enhance transparency and the tracking of queries.

Brand also offered a counterintuitive reason for not requiring a warrant before authorities search the records of U.S. persons collected under the law, saying it could result in less privacy for Americans.

"You would require more intrusive means to justify the use of less intrusive means, and that seems backwards to me," she said.

Brand's colleague on the civil liberties board, outgoing Chairman David Medine, said he believes a warrant would be useful, however, suggesting that one be required along with two other changes to Section 702: tightened rules for "upstream" collection selection terms and required disclosure about the number of Americans affected.

The utility of Section 702 is bound to be a key point of discussion as Congress mulls possible changes to the law. Last year, lawmakers banned the mass collection of domestic call records by passing the USA Freedom Act, after it became clear that program rarely if ever could be credited with thwarting terrorist plots, despite official claims it had prevented many plots in the wake of whistleblower Edward Snowden's 2013 surveillance disclosures.

Attorneys Matthew Olsen and Kenneth Wainstein, former government officials, testified on Tuesday that Section 702 has been a useful counterterrorism tool, allowing for the detection of schemes and discovery of terrorists. "We don't want to do anything to bring us back to the old days that led to 9/11," Wainstein warned.

Olsen pointed to the civil liberties board's 2014 report that said in "approximately" 30 cases, information collected under Section 702 was "the initial catalyst that identified previously unknown terrorist operatives and/or plots."

The factoid wasn't compelling for at least one senator, Democrat Patrick Leahy of Vermont, who was an influential proponent of last year's USA Freedom Act.

"I always worry what's behind the numbers," Leahy said. "We heard from the NSA about 52 attacks their [bulk phone record program] stopped. …The 52 became a dozen, which became five, which became part of one after the fact."

Though specific reforms seemed far from gaining consensus, there appeared to be broader agreement during the hearing that more details would be useful. "We're still missing a lot of facts about Section 702 implementation," said the committee's chairman, Iowa Republican Chuck Grassley.

Backdoor searches attracted greater public attention after a 2013 Reuters investigation revealed that the Drug Enforcement Administration sometimes engaged in "parallel construction" of criminal investigations to avoid disclosing where intelligence information came from, with sources at times appearing to include NSA intercepts.