The small portable hard drive was being kept as a backup, the National Archives explained in a question-and-answer document (PDF) on its Web site. It held copies of about 113 four-millimeter tape cartridges of "snapshots" of hard-drive contents of employees who left the Executive Office of the President.
Because the staff maintained White House entry information and electronic address books, the external drive contains personally identifying information including names and Social Security numbers of staff and visitors to the White House complex during the Clinton administration, the FAQ said.
National Archives staff began searching for the missing drive March 24 and notified senior officials at the agency on April 2. The National Archives' inspector general then opened a criminal investigation and the agency informed the U.S. Computer Emergency Readiness Team of the Department of Homeland Security, the White House Counsel's Office, staff of the House and Senate Oversight Committees, and a representative for former President Bill Clinton.
The National Archives will notify the individuals affected and offer them a year of credit monitoring. It is unknown how many people are affected, according to the FAQ.
"We do not know whether the drive was stolen, lost, or otherwise misplaced," the FAQ said.