The IPT's new interactive terror history map highlights cases of terror plots, terror financing and other radical activities in the United States during the past 20 years. Some of them are infamous, including the case of Fort Hood shooter Nidal Malik Hasan and the Hamas-supporting Holy Land Foundation for Relief and Development, both in Texas.

Others attracted less notoriety, like the plot by California prison inmates to attack Jewish and U.S. military targets.

You'll see three categories across the top of the map that can be turned off or on, depending on what you're interested in seeing.

One category identifies several mosques and Islamic centers. Given today's debates over mosque construction it is important to be clear about what the map represents. There are hundreds, if not thousands of mosques in the United States. We list but a few dozen.

The mosques and centers listed share one thing in common. It is not that all are radical, and many have not been involved in criminal activity. Rather, all have had contact with radical individuals and organizations at some point in the period covered.

At some locations, radical views have been espoused, extremists have spoken, or terrorist acts or groups have been supported.

One institution was home to an imam convicted of providing support to a U.S. designated Foreign Terrorist Organization (FTO). At another mosque, a future mastermind of a successful terrorist plot worshipped alongside other unknowing congregants. People at one mosque even helped the future 9/11 hijackers obtain Social Security numbers and driver's licenses. At others, imams have espoused rhetoric that is just plain violent.

In some of these examples, we learned about the activity only through the work of undercover law enforcement agents, informants and cooperating witnesses who helped root out extremists, foil terrorist plots and intercept terrorists' financial transactions.

Established Islamist groups have heatedly attacked law enforcement officials, casting their use of informants as part of a plot to set up Muslims. Though a staple of criminal investigations of all kinds, undercover operations should not breach the doors of a mosque, they say.

In the case of Dar Uloom Institute in Pembroke Pines, Florida, an undercover FBI agent foiled a plot by attendees to blow up a nearby energy facility. One individual who attended the mosque regularly, Imran Mandhai, recruited another mosque attendee, Shueyb Mosaa Jokhan, to carry out the plot. Both men pleaded guilty to conspiring to destroy property affecting interstate commerce. The FBI informant's work in this mosque uncovered another lead. Mandhai told the undercover agent that another man who attended the mosque, Adnan El-Shukrijumah, was a potential recruit for Osama bin Laden's plans to destroy more targets in South Florida.

Shukrijumah was recently indicted in the ongoing prosecution of a subway bomb plot in New York City.

Another informant's work in a Brooklyn mosque led to the conviction of Mohammad Ali Hasan Al-Moayad for conspiring to providing support to Hamas, a foreign terrorist organization. Al-Moayad bragged to an FBI informant about his work providing money, recruits and supplies to Hamas. According to the informant, Al-Moayad claimed that he received money for jihad from collections at Al Farouq mosque in Brooklyn, but officials were not sure that those giving money knew it would go to terrorists.

A cooperating witness at Dar us-Salaam Mosque in Seattle, Washington helped FBI agents nab Oussama Kassir, whom they suspected was trying to establish a terrorist training camp in nearby Bly, Oregon. The witness described Kassir's travels to Bly to inspect property designated to house the camp. Kassir also told the witness that he had trained for jihad in Afghanistan. In May 2009, Kassir was found guilty of providing material support to Al Qaeda.

Despite these examples, leaders of national Islamist organizations have balked at the use of informants. This message was made crystal clear by Hussam Ayloush, executive director of the Council on American-Islamic Relations (CAIR) - Los Angeles last year at an Anaheim, California mosque:

"We're here today to say our mosques are off limits. Our Koran is off limits. Our youth, who they [the FBI] try to radicalize, are off limits. Now is the time to tell them, 'We're not going to let this happen anymore.'"

On Monday, a jury in New York convicted two men who plotted to blow up fuel tanks at JFK airport. One of the conspirators planned to use a bank account for his mosque to store money for the plot. An informant played a key role in taping the conspirators discuss their plans and motivations.

These examples do not serve as a green light for the government to launch unconstrained investigations into Muslim communities, but rather show that Islamic religious institutions, just like any other institutions, are vulnerable to having contact with radical individuals and organizations.

FBI Informants in Mosques

In 2009, tensions between Islamist groups and the FBI came to a head when a coalition of organizations announced they considered cutting off ties with the FBI. One reason cited by that coalition, the American Muslim Task Force (AMT), was concern that the FBI is unfairly targeting American mosques for investigation.

The Muslim American Society (MAS) issued a press release reaffirming the AMT coalition's concerns regarding the "Infiltration of mosques and systematic manipulation of Muslim religious affairs," and the "Use of agent provocateurs to trap unsuspecting Muslim youth."

MAS Freedom Foundation leader Ibrahim Ramey said that, while his group rejects terrorism:

"...we also want law enforcement to understand that this should not be a pretext for demonizing an entire community or trying to turn the community against itself..."

Ayloush is one of the FBI's most outspoken critics. He has claimed that the FBI is "paying convicted felons to 'infiltrate' mosques to radicalize Muslim youths and instigate talks about terrorism." In an interview with Southern California Public Radio, Ayloush said the FBI has been "hiring shady characters and individuals to try to instigate against the Muslim community. And instigate acts of violence to ruin the reputation of the Muslim community."

At Masjid Omar Al Farouk in 2009, Ayloush reminded his audience that, "Just because there are bad apples, there are bad apples in our community, there are bad apples in the FBI, we should not start suspecting each other."

A new set of FBI guidelines issued in 2008 have been at the center of debate over informants. Critics claim the guidelines allow the FBI to send informants in without any purpose or predicate. The guidelines are stricter than detractors describe.

Current and former FBI officials also argue that the guidelines leave no room for the types of unwarranted investigations into mosques described by critics.

"Sending an asset into a mosque is not considered lightly, even in today's world," said Robert Blitzer, former Chief of the FBI's Domestic Counterterrorism Planning Section. Informants go where the suspects go:

"It really boils down to this, if the mosque is being used by individuals and groups who are the subjects of full counterterrorism investigations then the FBI has the authority to collect intelligence on the activities of the group or person while in the mosque."

Blitzer's assessment is pretty close to one given by current FBI Director Robert Mueller in 2009:

"We [the FBI] don't investigate places, we investigate individuals. To the extent that there may be evidence or other information of criminal wrongdoings, then we will ... undertake those investigations."

Steve Pomerantz, former assistant director of the FBI, told the IPT that some informants may not follow their handlers' very detailed instructions despite the guidelines. "That's the way it's supposed to work," he said, referring to the guidelines. "Can it break down? Yes, if the informant doesn't follow the instructions."

The FBI devotes a lot of time and resources to try to prevent these issues. Blitzer described "stringent vetting processes and procedures" to make sure that the information received from informants is reliable:

"These processes include many steps and tests, background investigations, and constant checking and double checking of information provided against records and other forms of reporting including human and technical source, other agency reporting, and foreign agency reporting."

Informants provide critical help for "the intelligence community [to] understand the intentions and actions of our enemies," said Blitzer. "Without them, we would be partially blind."

Pomerantz described informants as "the single most effective and useful investigative tool" and stressed that "a lack of [human intelligence] will only lead to more bad things happening."

Click here to take a look at the updated IPT terror history map. You'll see plenty of cases in which law enforcement stopped bad things from happening and a few instances in which terrorists still were able to strike.