'Federal employees who handle national security information are required to list some or all of their foreign contacts, depending on the agency, to receive high-level clearances. Investigators say that the hackers obtained many of the lists, and they are trying to determine how many of those thousands of names were compromised. The data breach is the third major foreign intrusion into an important federal computer system in the past year. In an earlier attack, some of the president's unclassified emails were apparently obtained by intruders.
'In classified briefings to members of Congress in recent days, intelligence officials have described what appears to be a systematic Chinese effort to build databases that explain the inner workings of the United States government. The information includes friends and relatives, around the world, of diplomats, of White House officials and of officials from government agencies, like nuclear experts and trade negotiators.
'“They are pumping this through their databases just as the N.S.A. pumps telephone data through their databases,” said James Lewis, a cyberexpert at the Center for Strategic and International Studies. “It gives the Chinese the ability to exploit who is listed as a foreign contact. And if you are a Chinese person who didn’t report your contacts or relationships with an American, you may have a problem.”
'Officials have conceded in the briefings that most of the compromised data was not encrypted, though they have argued that the attacks were so sophisticated and well hidden that encryption might have done little good.
'The first attack, which began at the end of 2013 and was disclosed in the middle of last year, was aimed at the databases used by investigators who conduct security reviews. The investigators worked for a contracting firm on behalf of the Office of Personnel Management, and the firm was fired in August.
'The broader attack on the personnel office’s main databases followed in December. That attack, announced last week, involved the records of more than four million current and former federal employees, most of whom have no security clearances.'