PHOTO: Lacey Russell/CNN
Now playing
01:41
You can use your face as ID for international flights
PHOTO: CNN
Now playing
01:26
Sen. Joe Manchin explains why he wanted changes to relief bill
Now playing
02:29
MS gov. encourages residents to wear masks despite dropping mandate
Now playing
01:21
Lawmaker fires back at Tucker Carlson's QAnon spin
Sen. Lisa Murkowski (R-AK) asks a question at a hearing of the Senate Health, Education, Labor and Pensions Committee on September 23, 2020 in Washington, DC.
PHOTO: Alex Edelman/Pool/Getty Images
Sen. Lisa Murkowski (R-AK) asks a question at a hearing of the Senate Health, Education, Labor and Pensions Committee on September 23, 2020 in Washington, DC.
Now playing
01:40
Trump plans to campaign against Sen. Murkowski in 2022
Biden 03062021
PHOTO: CNN
Biden 03062021
Now playing
02:28
'Help is on the way': Biden speaks after Senate passes relief plan
Now playing
03:04
Schumer: Nobody said it would be easy, but it is done
01 senate stimulus bill 210306
PHOTO: Senate TV
01 senate stimulus bill 210306
Now playing
01:47
Senate passes Biden's $1.9 trillion Covid-19 relief bill
WASHINGTON, DC - MARCH 05: Sen. John Cornyn (R) (R-TX) talks with Sen. Joe Manchin (D-WV) while walking to the U.S. Senate chamber for a vote March 05, 2021 in Washington, DC. The Senate continues to debate the latest COVID-19 relief bill.  (Photo by Win McNamee/Getty Images)
PHOTO: Win McNamee/Getty Images
WASHINGTON, DC - MARCH 05: Sen. John Cornyn (R) (R-TX) talks with Sen. Joe Manchin (D-WV) while walking to the U.S. Senate chamber for a vote March 05, 2021 in Washington, DC. The Senate continues to debate the latest COVID-19 relief bill. (Photo by Win McNamee/Getty Images)
Now playing
02:54
Axelrod breaks down Manchin's surprising move
sinema
PHOTO: CNN
sinema
Now playing
01:50
Senator's move has many on the internet outraged
PHOTO: FBI
Now playing
02:58
Trump State Department official charged in Capitol riot
WASHINGTON, DC - JANUARY 06: U.S. Sen. Paul Gosar (R-AZ) speaks on the floor of the House Chamber during a joint session of congress on January 06, 2021 in Washington, DC. Congress held a joint session today to ratify President-elect Joe Biden's 306-232 Electoral College win over President Donald Trump. A group of Republican senators said they would reject the Electoral College votes of several states unless Congress appointed a commission to audit the election results. (Photo by Drew Angerer/Getty Images)
PHOTO: Drew Angerer/Getty Images
WASHINGTON, DC - JANUARY 06: U.S. Sen. Paul Gosar (R-AZ) speaks on the floor of the House Chamber during a joint session of congress on January 06, 2021 in Washington, DC. Congress held a joint session today to ratify President-elect Joe Biden's 306-232 Electoral College win over President Donald Trump. A group of Republican senators said they would reject the Electoral College votes of several states unless Congress appointed a commission to audit the election results. (Photo by Drew Angerer/Getty Images)
Now playing
02:19
This is what Rep. Gosar was posting days before Capitol riot
John King Magic Wall 0305
PHOTO: CNN
John King Magic Wall 0305
Now playing
02:17
President Biden sending a team to the US-Mexico border
Senior Advisor to the President Jared Kushner  attends a press conference on September 4, 2020, in the Brady Briefing Room of the White House in Washington, DC. (Photo by Brendan Smialowski / AFP) (Photo by BRENDAN SMIALOWSKI/AFP via Getty Images)
PHOTO: BRENDAN SMIALOWSKI/AFP/AFP via Getty Images
Senior Advisor to the President Jared Kushner attends a press conference on September 4, 2020, in the Brady Briefing Room of the White House in Washington, DC. (Photo by Brendan Smialowski / AFP) (Photo by BRENDAN SMIALOWSKI/AFP via Getty Images)
Now playing
02:50
Jared Kushner disappears from Trump's inner circle
Rep john garamendi 0305
PHOTO: CNN
Rep john garamendi 0305
Now playing
02:33
Rep. Garamendi: Any lawmaker involved in Capitol riots ought to be thrown out of Congress
Protesters gather at Lincoln Park to demand the Emancipation Memorial be taken down on June 23, 2020 in Washington, DC.
PHOTO: Tasos Katopodis/Getty Images
Protesters gather at Lincoln Park to demand the Emancipation Memorial be taken down on June 23, 2020 in Washington, DC.
Now playing
03:01
Why some people want this Abraham Lincoln statue taken down
(CNN) —  

US Customs and Border Protection announced Monday photos of travelers and license plates were recently compromised in a data breach.

In a statement, CBP said it learned on May 31 that a subcontractor “had transferred copies of license plate images and traveler images collected by CBP to the subcontractor’s company network. The subcontractor’s network was subsequently compromised by a malicious cyber-attack.”

The agency has notified Congress and is working with law enforcement and cybersecurity entities to “determine the extent of the breach and the appropriate response,” according to the statement.

The images involve fewer than 100,000 people, according to initial reports, a CBP spokesperson said. The photographs were taken of travelers in vehicles entering and exiting the United States through a few specific lanes at a single land border port over one and a half months, said CBP.

“No other identifying information was included with the images,” said the spokesperson.

The photographs did not involve airline passengers, according to CBP.

The Washington Post first reported on the data breach.

CBP said its own systems had not been compromised, and the agency writes that, as of Monday, “none of the image data has been identified on the Dark Web or internet.”

The subcontractor “violated mandatory security and privacy protocols outlined in their contract,” according to CBP, which said it was unaware of the image copies transfers.

“CBP takes its privacy and cybersecurity responsibilities very seriously,” the statement reads, “and demands all contractors to do the same.”

Although the breach did not involve airline travel, it comes as CBP moves to expand its biometric data collection through facial recognition exit technology at airports, a move that has drawn scrutiny and concern from privacy advocates.

CBP has held at least a couple of meetings with privacy advocacy groups to discuss CBP’s biometric program.

Last fall, airport and federal officials showed off facial recognition technology, designed to replace the paper boarding pass and speed up the international flight boarding process.

John Wagner, the deputy executive assistant commissioner at CBP, said at the time that the technology is in response to a mandate from Congress that the Department of Homeland Security develop a system for tracking foreigners’ arrivals and departures from the United States.

“Everybody knows how to pose for a picture,” said Kevin McAleenan, who was then serving as CBP commissioner and now serves as the acting secretary of homeland security.

Privacy advocates pushed back on the move last year and are again arguing for a slow-down of CBP’s information collection efforts.

“This breach comes just as CBP seeks to expand its massive face recognition apparatus and collection of sensitive information from travelers, including license plate information and social media identifiers,” said American Civil Liberties Union spokeswoman Neema Singh Guliani in a statement.

“This incident further underscores the need to put the brakes on these efforts and for Congress to investigate the agency’s data practices,” Singh Guliani added. “The best way to avoid breaches of sensitive personal data is not to collect and retain such data in the first place.”

House Homeland Security Chairman Bennie Thompson said he plans to hold hearings next month on the agency’s use of biometric information.

“Government use of biometric and personal identifiable information can be valuable tools only if utilized properly. … We must ensure we are not expanding the use of biometrics at the expense of the privacy of the American public,” the Mississippi Democrat said in a statement.

This story has been updated.

CNN’s Gregory Wallace contributed to this report.