Since Andrew Joseph Stack III piloted his plane into the Echelon I office building in Northwest Austin in his self-described effort to exact a "pound of flesh" from the Internal Revenue Service, a debate has raged as to how to classify his shocking crime.

Some people have dismissed Stack as a wing-nut who simply snapped. Others have described him as an extremist or a terrorist. A few have even tried to defend his actions.

In the days since his shocking act, though, a clearer picture has emerged. In his online manifesto, Stack's hatred of the government and desire for violence is manifest. Stack expressed a sentiment common to many domestic extremists — a dream that the "American zombies (would) wake up and revolt."

Stack hoped his action would cause a "standard, knee-jerk government reaction that results in more stupid draconian restrictions," which in turn would cause people to rise up. Violence, for Stack, "not only is the answer, it is the only answer."

With such sentiments, Stack and his crash closely fit the profile of a "lonewolf" terrorist. Lone-wolf terrorists are individuals who commit violent acts on their own without belonging to an organized extremist or terrorist group or cell.

Lonewolves have been deadly in recent months, with perpetrators coming from backgrounds including white supremacists, Muslim extremists and anti-abortion extremists.

In 2009, more than 30 extremist-related killings occurred in the U.S. Of these, a number bore the hallmarks of "lonewolf" attacks, including Maj. Nidal Hassan's shooting rampage at Fort Hood in November, as well as two shootings in June: white supremacist James von Brunn's murder of a security guard at the U.S. Holocaust Memorial Museum in Washington, D.C., and the murder of an American soldier at a military recruiting center in Little Rock, Ark.

Most terrorist plots and conspiracies in the U.S. are detected and prevented by law enforcement. Lonewolves, though, are feared precisely because their acts are so difficult to stop.

When extremists work alone, there are fewer opportunities to detect them in advance. Some lonewolves, such as Ted "Unabomber" Kaczynski and Olympic Park bomber Eric Rudolph, have been able to carry out multiple terrorist acts before being caught. Moreover, lone-wolf actions tend to be particularly deadly, as causing human casualties is usually the primary goal of the perpetrator.

Analysis of lone-wolf incidents in recent decades reveals certain patterns. Most lone-wolf perpetrators are men and tend to be either in their early-tomid-20s or middle-aged. Though motivated by extremism, they are typically involved only at the periphery of extremist movements, as was Stack, who had brushes with the tax protest movement.

Many lonewolves may have "loner" personalities. Often, they face intense personal stress or social difficulties, or they suffer from mental illness. Experience also suggests that their violence is often preceded by days to weeks of brooding, fantasizing or planning.

There are no easy ways to prevent lone-wolf violence.

Sometimes friends or relatives might spot signs of intense stress that suggest a possibility for violence; police should always take such warnings seriously. Occasionally, members of an extremist movement might warn others in the movement to stay away from someone who seems dangerous and unpredictable.

It is also sometimes possible to mitigate lone-wolf violence that does occur, if police are trained in "active shooter" tactics that have been developed in recent years. Every police department should be familiar with such tactics — they can save lives.

But there also needs to be recognition and awareness that lone wolves may act alone, but do not do so in a vacuum. Their actions can be influenced or inspired by many factors. These can include the high-profile acts of other lonewolves, as well as the rhetoric and ideology of extremist groups, which often influence the targets lone wolves choose.

These groups and their ideas are more powerful than ever, thanks to their ability to spread their ideas through the Internet. There are other Joseph Stacks out there right now, imbibing this extremism and anger who might eventually be triggered to act out against the targets of their own hatred, whether it be the government or people of a race or religion unlike their own.

The consequences, however, affect all of us.

The Anti-Defamation League, founded in 1913, is the world's leading organization fighting anti-Semitism through programs and services that counteract hatred, prejudice and bigotry.