US Immigration and Customs Enforcement said on Wednesday that it had inadvertently posted to its website the personal information of more than 6,000 people in its custody.

The information included names, nationalities, detention centers where the people were held and unique numbers used to identify them in government records, according to Human Rights First, an advocacy group that discovered the leak on Monday.

All 6,252 people whose identities were exposed had earlier expressed fear of persecution if courts denied their bids to remain in the US and were returned home, according to Human Rights First.

Eleanor Acer, the group’s senior director for refugee protection, said she worried that detainees or their families might be in danger in their home countries.

“In some countries people are targeted, retaliated against for seeking asylum,” the Associated Press reported Acer saying.

Ice said an Excel spreadsheet was erroneously posted “while performing routine updates” and was up for about five hours. It said it deleted the information 11 minutes after being notified.

“Though unintentional, this release of information is a breach of policy and the agency is investigating the incident and taking all corrective actions necessary,” Ice said in a statement.

It said it would tell detainees or their attorneys of the leak, which was first reported by the Los Angeles Times.

“This will allow noncitizens or their attorneys-of-record to determine whether the disclosure may impact the merits of their protection claim,” an Ice spokesperson said.

The Los Angeles Times also reported that the government will notify individuals who downloaded the information that they should delete it, and that Ice is monitoring the internet for potential reposting.

Diana Rashid, a managing attorney of the National Immigrant Justice Center, told the paper her organization was concerned over the disclosure of the identity of one of her clients, a Mexican woman.

“We are deeply concerned about our client’s safety after Ice publicly shared this very sensitive information about her and thousands of others like her,” Rashid said.

“She is seeking protection from removal because she fears persecution if returned to her country of origin. Revealing this information makes her more vulnerable to the persecution and abuses she fears if deported.”

Heidi Altman, director of policy at the National Immigrant Justice Center, echoed similar sentiments, telling the paper: “The US government has a crucial obligation to hold asylum seekers’ names and information in confidence so they don’t face retaliation or further harm by the governments or individuals whose persecution they fled.

“Ice’s publication of confidential data is illegal and ethically unconscionable, a mistake that must never be repeated.”