Michelle Ledgister was hopping mad over losing a property tax exemption on a home she owns and rents out near Boca Raton, Fla. Sure, she lives in Maryland near the National Institutes of Health, where she holds an administrative position at the National Institute of Allergy and Infectious Diseases. She didn't see why that should keep her from getting the real estate tax breaks that a Florida resident would be entitled to.

So, according to police, she called the Broward County property appraiser's office in Fort Lauderdale late last month and left a voicemail message: "It's Michelle Ledgister. I must commend your skillful sleuths in knowing where the main campus of NIH is located. But what they didn't tell you is that NIH is located where infectious agents are, and you guys now have anthrax spores once again, so do be careful. Toodles."

Bad move, if she did it. The penalty for making a false terrorism threat is up to five years in federal prison and up to $250,000 in fines. (Her property taxes, had she just paid them, more than doubled without the exemption, but only from $1900 to $4200, says Bob Wolfe, spokesman for the assessor's office.) And people are touchy about anthrax spores in Ft. Lauderdale, which is only 21 miles from Boca Raton, the place where one of the five people who died in the October 2001 anthrax letter attacks worked.

What makes Ledgister's case particularly unusual is that "most people don't identify themselves," says Sundara Vadlamudi, a research associate at the Monterey Institute of International Studies' Center for Nonproliferation Studies. Since the mid-1990s, the center has recorded 578 anthrax hoaxes, 345 of them perpetrated inside the United States. The few anthrax hoaxers who do identify themselves are usually playing a joke, not making a real threat, says Vadlamudi. In October 2001, for example, a Pennsylvania man sent a powder-filled letter to his aunt as a practical joke, notifying her beforehand to expect it. Unfortunately for his aunt and him, a letter carrier noticed white powder on the envelope and alerted postal inspectors.

Still, not all self-identified anthrax hoaxers are jokesters, Vadlamudi says. In November 2001, an immigrant from India gave two suspicious-looking envelopes to a National Guard soldier standing outside Grand Central Station in New York City, hoping to get deported back to India because he didn't have the money to pay for the trip. About the same time, a mail carrier in Virginia sprinkled baby powder inside a piece of bulk mail she broke open in order to make her supervisors take the anthrax threat more seriously.

Courts have given a wide range of sentences for anthrax hoaxes, Vadlamudi notes: severe ones for felony charges when the intent was to create a scare, but shorter ones, often for misdemeanor convictions, when the intent was to make a joke. But Ledgister can't expect lenient treatment, says Dan Stiller, her Federally appointed lawyer, because she is charged under a 2004 Federal terrorism law that specifically targets hoaxes and mandates the stiff sentence she faces.

Stiller said earlier this month that Ledgister hasn't decided whether she'll plead guilty or innocent, and that she was unavailable for comment. "Ms. Ledgister fully understands the gravity of this situation, and it's been a humiliating week for her."

Wolfe said the appraiser's staff feels badly for Ledgister. "I assume this lady's career is over, and I'm sure she feels awful about it, too," he said. "But it's not a laughing matter in today's world, especially since we've had an incident in Florida with anthrax."