U.S. investigators handling the data breach that resulted in the personal information of 4 million federal workers being stolen now fear that Chinese hackers may have also taken off with a database of foreigners with ties to the U.S. government, a report Wednesday said.

That valuable data, which includes the names of Chinese individuals with connections to U.S. federal employees, could put the lives of many at risk of being blackmailed by the Chinese government or targeted for retaliation, according to the New York Times.   

All federal employees are required to disclose the names of foreigners with whom they have ties, either as friends, relatives or in any other matter. Those contacts are then kept in lists, some of which were accessed by Chinese hackers when they breached the databases of the U.S. Office of Personnel Management and the U.S. Interior Department. Investigators, however, do not yet know exactly how many names were compromised. 

Chinese hackers gained access into the record of the two federal bodies last December, but their cyberattack went undetected by the U.S. until April. The breach was not disclosed until last week when the U.S. Department of Homeland Security announced it. It is believed that the Chinese government is using the stolen information to create a database with which it can figure out the inner working of the U.S. government.

According to the Times, the data stolen from the Office of Personnel Management and the Interior Department was not encrypted, meaning anyone who gains access to the files can see the information without needing a key or any kind of code. Encrypting files is a standard procedure followed by most organizations that keep databases of sensitive information.