Tighter background checks and improved security would help prevent a repeat of the deadly 2001 anthrax attacks, military officials said Thursday, while acknowledging there are no guarantees. It was five months ago that an Army biodefense lab scientist, Bruce E. Ivins, committed suicide after being named the prime suspect in those attacks. "I can't say for certain it could not happen today," Army Maj. Gen. Robert Lennox, assistant deputy chief of staff for operations and training, told reporters. "But it would be much more difficult." He said there are more hurdles now before someone could remove a biological agent or toxin from a lab and seek to use it.