WASHINGTON—In what they described as one of the U.S. military's "most serious" security breaches to date, Pentagon officials acknowledged Friday that they could not confirm the whereabouts of a LaCie d2 Quadra external hard drive containing nearly 500 gigabytes of crucial materials, including all their favorite movies and several seasons of Entourage. "It could take months to recover the critical information we have lost," announced Adm. Michael Mullen, adding that the hard drive represents nearly 200 man-hours of confidential downloads. "All we've got left now is Brig. Gen. Nowak's DVD boxed set of The Lord Of The Rings and YouTube." The department's inspector general has vowed a full investigation, and military police have tightened security around other stores of highly sensitive data, including the file cabinet with all the takeout menus.