U.S. Immigration and Customs Enforcement (ICE) accidentally leaked the personal information of more than 6,000 people in its custody on its website for about five hours, according to NBC 5.

According to Human Rights First, the advocacy group that discovered the leak said the website listed the names, nationalities, and detention centers where the people were held. The unique numbers used to identify them in government records were also leaked. In total, 6,252 asylum seekers’ information was posted on the website.

Eleanor Acer, senior director of refugee protection at Human Rights First, said she is concerned that detainees or their families might be in danger in their home countries. Immigrants often fear that the gangs, governments, or individuals who persecuted them back home will find out they sought protection in the U.S. The Los Angeles Times reported that some unlawful migrants listed were from Iran, Russia, and China.

“In some countries, people are targeted, retaliated against for seeking asylum,” Acer said.

ICE said the information, listed on an Excel spreadsheet, was accidentally posted during routine website maintenance. After being notified, the agency took 11 minutes to delete the information from its website, according to NBC 5.

“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 is notifying non-citizens impacted by the disclosure,” the agency said in a statement.

Los Angeles Times immigration policy reporter Hamed Aleaziz said the leak was “unprecedented,” and it is unclear whether any outside investigations will occur regarding how the leak occurred.

Aleaziz said ICE affirmed it would not deport any immigrants until it was clear whether any leaked information would affect their asylum cases.

ICE said it is actively monitoring the web to see if the information obtained is posted anywhere and will notify the lawyers of any individuals listed in the leak.