The strain was probably stolen from one of our labs years ago. Who really knows how many countries have the Ames strain nowadays? Our country is still a sieve even now, and was far worse back during the Clinton years. You'd have a heart attack if you saw some of the freaks who got security clearances back in those days.
Heck, we sent it to anyone that asked for it.
Anyone and everyone interested in the subject.
WMD was not a issue then and nobody thought the Anthrax would ever qualify to be a wmd.
Some still don't, but the stuff that went to the Senate office was pretty scary.
Trouble is, anti-bacterial treatment is available and fairly cheap. Mass casualties with anthrax has really never been a possibility. It sure made a terror weapon though.