A security camera recorded the man wearing dark sunglasses and a hooded sweat shirt as he walked by Boston's Symphony Hall on Feb. 9 and dropped a cardboard tube marked "Anthrax Beware" at the door.
Emergency medical crews raced to the site, firefighters cordoned off the area, police halted traffic, and life came to an anxious halt until a hazmat team signaled the all-clear: The tube was empty.
In the 7 1/2 years since America's worst bioterrorist attack -- when letters laced with anthrax spores killed five people, closed Congress and the Supreme Court, and crippled mail service for months -- U.S. agencies have spent more than $50 billion to beef up biological defenses.
No other anthrax attacks have occurred.
But a flood of anthrax hoaxes and false alarms have raised the cost considerably through lost work, emergency evacuations, decontamination efforts, first-responders' time and the emotional distress of the victims.
That, experts say, is often the hoaxer's goal.
"It's easy, it's cheap, and very few perpetrators get caught," said Leonard Cole, a political scientist at Rutgers University in Newark, N.J., who studies bioterrorism. "People do it for a sense of power."
Among the recent targets: nearly all 50 governors' offices; about 100 U.S. embassies abroad; 52 banks; 36 news organizations; ticket booths at Disneyland; Mormon temples in Salt Lake City and Los Angeles; town halls in Batavia, Ohio, and Ellenville, N.Y.; a funeral home and day-care center in Ocala, Fla.; a sheriff's office in Eagle, Colo.; and homes in Ely River, N.M.
The FBI has investigated about 1,000 such "white powder events" as possible terrorist threats since the start of 2007, spokesman Richard Kolko said. The bureau responds if a letter contains a written threat or is mailed to a federal official.
"Some of these knuckleheads think because they're not sending a dangerous substance, it's not a crime," Kolko said. "But it is a crime. We don't treat a hoax as a joke."
In one recent case, emergency crews cleared and sealed a Department of Homeland Security office in Washington after a senior official, who had received a package at home containing white powder and a dead fish, brought it to work for inspection.
The contents proved harmless, and the official, who collects intelligence on weapons of mass destruction, remains a department employee, a spokeswoman said.
Other cases, however, are more worrisome.
The FBI is trying to figure out who mailed about 150 letters late last year that contained powder and threatening notes. The envelopes were sent from the Dallas area to U.S. embassies in various countries and to most U.S. governors.
"It's possible that the final two or three letters went to governors who are no longer in office," said Mark White, an FBI spokesman in Dallas. "They may still trickle in."
One letter, for example, was addressed to former Massachusetts Gov. Mitt Romney, who left office two years ago. When it arrived in Boston, someone marked "return to sender" on the envelope and popped it back in the mail. The return address was the FBI office in El Paso.
White powder spilled out when an FBI clerk there opened it Feb. 12. Anxious officials emptied the Federal Justice Center, sending more than 300 FBI, Drug Enforcement Agency and other law enforcement personnel home. The powder proved to be baking soda, White said.
The Justice Department was able to bring criminal charges in two other high-profile cases.
Richard L. Goyette, 47, pleaded not guilty Thursday in Amarillo, Texas, to charges of mailing 65 threatening letters to banks and other financial institutions in October. The envelopes contained white powder and a warning that the recipient would die within 10 days.
According to prosecutors, Goyette was distraught after losing $63,525 when federal regulators seized Washington Mutual Bank and placed it in receivership. The FBI said it traced him through angry e-mails that he sent to the banks.
If convicted, Goyette would face a maximum five-year prison term on each charge, although sentencing guidelines would lower the total.
The powder was identified as calcium carbonate, which is used in antacids and blackboard chalk.
In the second case, a federal grand jury in Sacramento indicted Marc M. Keyser, 66, in November for allegedly mailing hoax letters; 120 of them went to newspapers, a member of Congress, a McDonald's, a Starbucks and other targets.
Each contained a CD labeled "Anthrax Shock and Awe Terror," and a packet of granular material bearing a biohazard symbol and the words "Anthrax Sample," the FBI said. The substance was harmless.
Keyser's home address was on several mailings. After his arrest, prosecutors told a judge that Keyser had hoped the publicity would raise concern about anthrax and draw attention to his blog and novel. He has pleaded not guilty.
Cases that result in charges are the exception, however.
In the last two fiscal years, records show, U.S. postal inspectors responded to more than 5,800 reports of letters and packages containing suspicious substances. Only a few dozen cases have resulted in arrests.
"We try to use common sense," said Peter Rendina, spokesman for the U.S. Postal Inspection Service. "We know there are cases where Grandma is sending her favorite muffin recipe and doesn't mean to be a threat."
Scientists disagree over whether the nation is more vulnerable to an anthrax attack today than it was in 2001. (The FBI blames that attack on Bruce E. Ivins, an anthrax researcher at a federal biodefense facility who committed suicide in July.)
The U.S. Postal Service in 2003 installed devices to check for airborne pathogens or poisons at the nation's 271 mail processing and distribution centers. They have yet to detect a threat, Rendina said.
But the boom in biodefense spending carries a danger. Some experts fear that a tenfold increase in laboratories authorized to work with dangerous bioagents increases the risk of leaks. More than 7,200 scientists now are approved to work with anthrax, far more than in the past, creating security risks.
"I think all our screaming about bioterrorism has been counterproductive," said Milton Leitenberg, a University of Maryland scholar who has written extensively about biological weapons. "It's a hard balance to strike."
Boston police felt the same way after the incident at Symphony Hall last month.
An address label on the DHL tube led detectives to a local man, who said he had tossed it in a Dumpster. Police never figured out who picked it up and wrote "Anthrax Beware" on it, or why.
"Happily, there was nothing to it," said Jill McLaughlin, a police spokeswoman. "We've got enough problems without an anthrax scare."