More than 600 children were "recycled" by human traffickers looking to exploit loopholes in the American immigration system during the past fiscal year, a federal immigration official told lawmakers Wednesday.

At a hearing to evaluate border statistics during fiscal year 2019, which ended Sept. 30, Immigration and Customs Enforcement acting Deputy Director Derek Benner told the Senate Homeland Security and Government Affairs Committee that the figure was a result of a DHS initiative called "Operation Noble Guardian" to identify situations "where fraudulent families were released into the interior, and then the children were separated from those unrelated adults and they were taken to an airport and flown back" to Central America.

"We've identified over 600 children that have been recycled in this methodology," Benner explained. "We interviewed several of the children as they were departing the United States, and some of them had indicated they've made the trip as many as eight times with separate, unrelated adults every time."

Benner explained during his opening statement that the recycling process is migrants seeking to use children as "passports" when apprehended at the border so that they can be released into the United States interior rather than face deportation at the border.

The Trump administration has made efforts to combat the practice of human smugglers using children to evade detention, most notably through an executive order from earlier this year that allowed federal authorities to keep family units in detention past the court-set mandate. However, that effort is currently facing a challenge in the federal court system and is expected to end up before the Supreme Court.

Benner also explained that widespread knowledge of the use of rapid DNA testing to weed out fraudulent family claims at the border has been helpful in cutting down on the practice.

"We've found, with rapid DNA, about a 13 to 15 percent hit rate on fraudulent families," Benner told committee Chairman Ron Johnson (R-Wis.). "Now initially, Senator, when we first got there during the height of the crisis, we were showing showing percentages that were above 20 percent, 25 percent, because the amount of fraud was rampant."

A pilot DNA testing program at the border found that roughly 30 percent of of suspected fraudulent family units were not genetically related, according to a Washington Examiner report from May.

"Word spreads," Benner explained to the Senate panel. "The cartels are the best advertisers of what works and what doesn't, and within a short period of time, it was getting back to the organizations that they needed to pivot their operations."

Following Benner's explanation, Johnson clarified to the hearing room that the 600 statistics "are people we catch, and we don't even know how many people we don't. We don't understand the magnitude of this problem."