Sometime between October 2008 and March 2009 the National Archives lost a hard drive with a terabyte of sensitive information from the Clinton-era White House, according to congressional officials.

The hard drive contained “an as-yet-unknown amount of personally identifiable information of White House staff and visitors,” according to a statement from the archives. A terabyte of data is the equivalent of millions of books.

Information on the hard drive includes names, addresses and Social Security numbers of White House employees and visitors, including one of former Vice President Al Gore’s three daughters.

The statement also said that the agency “takes very seriously the loss of an external hard drive that contained copies of electronic storage tapes for the executive office of the president of the Clinton administration.”

Though the breach of personal information is indeed very serious, of greater consequence is the loss of Secret Service and White House operating procedures, as well as logs of events, social gatherings and political records.

Rep. Darrell Issa of California said the hard drive had been stored in a secure area, but was moved to an unsecured workspace, presumably so the Clinton administration’s information could be converted to a digital records system, as asserted by an unnamed aide.

The archives inspector general said the door to the area was frequently left open for ventilation and at least 100 badge-holders, janitors, visitors, interns and anyone else on their way to the bathroom had access to the area according to Issa.