Carol Keller of Revere was alarmed to learn last fall that someone was making purchases with her debit card. What she didn’t know was that weeks earlier her personal and medical information had been stolen when a Pentagon contractor left 25 computer tapes in the backseat of a Honda Civic in a San Antonio parking garage. Keller, who is married to a disabled Air Force veteran and relies on the Pentagon-run health insurance program called TRICARE, is among nearly 5 million military personnel, retirees, and their families - including nearly 70,000 across New England. She has joined a lawsuit seeking damages.