A suicidal pilot's attack on an Internal Revenue Service building in Austin, Texas, last week was the worst but hardly the lone example of threats against the tax agency, according to the U.S. government.
The number of threats against the tax-collection agency has increased significantly in recent years, Treasury Department officials said.
There were 1,200 threats and assaults against IRS employees from 2001 to 2008, resulting in 195 convictions, according to officials. J. Russell George, the Treasury inspector general for tax administration, said threats that once averaged 170 or so a year are now up to about 900.
Some recent examples: a man in tax trouble hired someone to kill an IRS employee in Tampa, Fla.; an Alabama man tried to use his car as a deadly weapon by driving into an IRS building; and two arsonists in Colorado Springs, Colo., used a sledge hammer to break into and then torch an IRS building.
Some threats are so serious that armed escorts join IRS employees at meetings with potentially dangerous taxpayers.
The agency deployed such protection for IRS employees 23 times from April to September last year under a new initiative, according to Treasury officials. It's not unusual, the IRS said, to dispatch a protection agent once a week for one of its 90,000 employees.
Fathali Moghaddam, a Georgetown University psychology professor, blamed the rise in these kinds of threats on a difficult economic climate that leads to discontent and frustration in people. There's also global insecurity because of the greater interconnectedness of the modern world, he said.
"There are all kinds of threats against us, and citizens have a social contract," Moghaddam said. "They ask, 'Is the government protecting us from economic downturn, from terrorism?' There is a feeling that authorities are not doing enough, that Americans are paying their tax dollars and are looking for government to do something, but they look incompetent."
Inspector general George said, "There is a direct rise between enhanced enforcement efforts and direct threats made against IRS employees."
Given last week's attack, he said, "I have to say I am concerned about copy cats."
Treasury Secretary Timothy Geithner and IRS Commissioner Doug Shulman on Monday toured the remains of the damaged IRS building in Austin, where nearly 200 IRS employees worked. They expressed condolences to the family of the IRS employee who died in the attack.
"I just want to say how proud we are of the men and women of the IRS," Geithner said. "We came to show them respect and support."
ABC News' Jack Cloherty and Jason Ryan contributed to this report.