If hoaxsters thought they could get away with exploiting the chaos spawned by the Sept. 11 terror attacks, then Attorney General John Ashcroft had a warning for them Tuesday. 

Calling faked anthrax attacks "grotesque transgressions of the public trust," Ashcroft said at a news conference that such hoaxes would be prosecuted as federal crimes. He also announced the first arrest, that of a Connecticut man who seemed to be playing an office joke. 

"It should be painfully obvious to every American today that the threat of bioterrorism is no joking matter," Ashcroft said, adding that hoaxes "create illegitimate alarm in a time of legitimate concern. Terrorism hoaxes are not victimless crimes but are the destructive acts of cowards." 

At the same conference, FBI Director Robert Mueller said that while there's no evidence linking the real anthrax attacks to "organized terrorism," there's also no reason to rule out such a connection. 

Letters containing the potentially deadly anthracis bacterium have been sent to locations in New York City, Washington, D.C., Florida and Nevada. One Florida man died Oct. 5, and the number of confirmed cases of anthrax exposures has increased nearly every day since. 

Mueller said there was similar handwriting in the letters sent to Senate Majority Leader Tom Daschle in Washington and NBC News in New York, both of which contained anthrax spores. Both letters were postmarked in Trenton, N.J., on Sept. 18. 

Mueller added that threats of attack against the United States have not diminished since last week, when his office issued a warning about further terror activity. 

With that in mind, the hoaxes riding on the back of palpable terrorism fears have become a serious headache for law-enforcement officials, who are overwhelmed by calls from nervous Americans who fear they might be infected. 

The FBI has received more than 2,300 reports of incidents or suspected incidents involving anthrax. Most of the them have been false alarms or practical jokes, Mueller said.

The FBI also arrested two people outside New York who had sent hoax anthrax letters, officials said separately. 

Not only are the hoaxes forcing authorities to squander valuable time and money, but they have proven costly for companies that have to shut down operations. The anthrax scare in Connecticut cost one state government office $1.5 million, a federal law-enforcement official said. 

In that case, state Department of Environmental Protection worker Joseph Faryniarz was charged Monday with making false statements during an anthrax scare. 

Faryniarz told agency security guards on Oct. 11 that he found a powdery substance on a paper towel under some paperwork near his computer. On the towel was written "ANTHAX," according to a criminal complaint. Security officials alerted the police and all 800 agency employees were evacuated.

Faryniarz was given a chance to clear up the matter without jeopardizing his job. He told FBI agents that he thought the incident was a "bad joke" and said two colleagues might be involved.

He later acknowledged that he had been untruthful and said he knew the incident was a hoax even before the FBI arrived on the scene because another individual not named in the complaint had claimed responsibility.

"The complaint [by the U.S. Attorney in Connecticut] charges that [Faryniarz] knew the incident was a hoax but reportedly stood by silent as 800 employees were evacuated and 12 employees were forced to disrobe and be washed down with a decontamination solution," Ashcroft said. 

Federal law allows a fine of up to twice the losses in such hoaxes. The state agency estimated that in addition to the two-day, $1.5 million cost of the disruption, decontamination will cost about $40,000. 

Mueller said the FBI may not have moved fast enough to investigate a suspicious letter sent to NBC in New York that turned out to test negative for anthrax.

"There were missteps at the outset," said Mueller. "We did not, as quickly as we would have liked, analyze an initial specimen from a letter that turned out to be negative."

He said the problem did not affect the investigation but added that FBI field offices have been instructed to make sure suspicious materials are analyzed promptly.

The Associated Press contributed to this report.