Her recent WSJ piece highlights the danger of Islam being propagated in US prisons, a problem which is too little known. Of course, the biggest Islam danger comes via immigration by which thousands of potential hostiles enter annually — a policy that should be ended.

But prisons offer a captive audience of angry young men who may be open to hearing an excuse for violent behavior. Some inmates are receptive to the belief that robbery and murder are acceptable when done by Muslims against infidels for the glory of Allah: just follow your violent actions with an Allahu Ackbar and it’s all cool. Islam is therefore the ideal religion for criminals.

One disturbing example of a prison convert is Alton Nolen, who beheaded coworker Coleen Hufford in an Oklahoma food plant after he was fired last fall. He had demanded that she convert to Islam and her refusal was an excuse to murder her according to Islam scripture.

Ayaan points out that some of the imams doing prison ministries are dangerous and dedicated to jihad, yet are paid by the government to teach Islam behind bars to persons already inclined toward violence.

America’s Academies for Jihad, By Ayaan Hirsi Ali, Wall Street Journal, March 31, 2015

A radical imam threatened me with death—and was later hired to preach in U.S. prisons. I was surprised, but I shouldn’t have been.

Less than a year after I moved to the United States in 2006, I was asked to speak at the University of Pittsburgh. Among those who objected to my appearance was a local imam, Fouad El Bayly, of the Johnstown Islamic Center. Mr. Bayly was born in Egypt but has lived in the U.S. since 1976. In his own words, I had “been identified as one who has defamed the faith.” As he explained at the time: “If you come into the faith, you must abide by the laws, and when you decide to defame it deliberately, the sentence is death.”

After a local newspaper reported Mr. Bayly’s comments, he was forced to resign from the Islamic Center. That was the last I would hear of him—or so I thought.

Imagine my surprise when I learned recently that the man who threatened me with death for apostasy is being paid by the U.S. Justice Department to teach Islam in American jails.

According to records on the federal site USASpending.gov and first reported by Chuck Ross of the Daily Caller, the Federal Bureau of Prisons awarded Mr. Bayly a $10,500 contract in February 2014 to provide “religious services, leadership and guidance” to inmates at the Federal Correctional Institution in Cumberland, Md. Ten months later he received another federal contract, worth $2,400, to provide “Muslim classes for inmates” at the same prison.

This isn’t a story about one problematic imam, or about the misguided administration of a solitary prison. Several U.S. prison chaplains have been exposed in recent years as sympathetic to radical Islam, including Warith Deen Umar, who helped run the New York State Department of Correctional Services’ Islamic prison program for two decades, until 2000, and who praised the 9/11 hijackers in a 2003 interview with this newspaper.

That same year, the Senate Subcommittee on Terrorism held hearings on radical Islamic clerics in U.S. prisons. Committee members voiced serious concerns over the vetting of Muslim prison chaplains and the extent of radical Islamist influences. Harley Lappin, director of the Federal Bureau of Prisons at the time, said that “inmates are particularly vulnerable to recruitment by terrorists,” and that “we must guard against the spread of terrorism and extremist ideologies.”

Yet it is not clear what measures—if any—were taken in response to those concerns.

Testifying in 2011 before the House Committee on Homeland Security, Michael P. Downing, head of the Los Angeles Police Department’s Counterterrorism and Special Operations Bureau, said that in 2003 it was estimated that 17%-20% of the U.S. prison population, some 350,000 inmates, were Muslims, and that “80% of the prisoners who convert while in prison, convert to Islam.” He estimated that “35,000 inmates convert to Islam annually.”

Patrick Dunleavy, retired deputy inspector of the Criminal Intelligence Division at the New York State Department of Corrections, said in testimony that prison authorities often rely on groups such as the Islamic Leadership Council or the Islamic Society of North America for advice about Islamic chaplains. Yet those groups can and have referred individuals not suited to positions of influence over prisoners. As Mr. Dunleavy pointedly testified: “There is certainly no vetting of volunteers who provide religious instruction, and who, although not paid, wield considerable influence in the prison Muslim communities.”

The problem isn’t limited to radical clerics infiltrating prisons. Radical inmates proselytize and do their utmost to recruit others to their cause. Once released, they may seek to take their radicalization to the next level.

Kevin James formed the Assembly of Authentic Islam while in New Folsom State Prison in California. In 2004 James recruited fellow prisoner Levar Washington to his cause. After being released, James developed a list of possible targets including an Israeli consulate, a Jewish children’s camp in Malibu, Los Angeles International Airport and a U.S. military recruiting station in Santa Monica. The two men pleaded guilty to conspiracy charges; Washington was sentenced to 22 years in 2008, James to 16 years in 2009.

Michael Finton converted and radicalized in an Illinois state prison while serving time for aggravated assault. Finton wanted to attack a federal government building and spoke of the need to attack members of Congress. He pleaded guilty to attempted use of a weapon of mass destruction and was sentenced to 28 years in prison in 2011.

In 2009 the “Newburgh Four”—James Cromitie, Laguerre Payen,David Williams and Onta Williams—were arrested for plotting to bomb synagogues in New York City. The men also intended to shoot down military aircraft with Stinger missiles. All four had converted to Islam in prison, where they developed radical sympathies. The men didn’t know each other while in prison but met after their release while attending a local mosque connected to a prison ministry. All four were convicted on conspiracy charges and received 25-year sentences in 2011.

In January 2010 John Kerry, who was then chairman of the Senate Foreign Relations Committee, released a report warning that “three dozen U.S. citizens who converted to Islam while in prison have traveled to Yemen, possibly for al Qaeda training.”

Europeans have known for some time that prisons can be breeding grounds for Islamists. The British “shoe bomber,” Richard Reid, is thought to have been radicalized while in prison for smaller crimes. Two of the gunmen in the Paris terror attacks in January—Chérif Kouachi and Amedy Coulibaly—came under the religious influence of Djamel Beghal, a convicted terrorist and charismatic Islamist, when serving prison sentences. Mohamed Merah, who killed three soldiers, three small children and a rabbi at a Jewish school near Toulouse, France, in 2012, apparently became a jihadist while in jail. The list is depressingly long.

The problem is that experts tend to be concerned about prison radicalization only to the extent that it ultimately results in some type of violent attack. Yet there are good reasons to be concerned about the inmates who come to cherish a radical interpretation of Islam while refraining—for the time being—from the use of violence. The boundary between nonviolent and violent extremism is much more porous than conventional wisdom allows.

What can be done to stop prisons from becoming academies of jihad? Here are four suggestions:

1) Choose better partners than the Islamic Society of North America and the Islamic Leadership Council to screen prison chaplains. The American Islamic Forum for Democracy, founded and led by M. Zuhdi Jasser, a medical doctor and former lieutenant commander in the U.S. Navy, would be a good choice.

2) Prevent radical clerics from coming into prisons to spread their message to susceptible inmates.

3) Ban radical Islamist literature from being disseminated in U.S. prisons.

4) Stop placing inmates in proximity to radicalized mentors.

The fact that Fouad El Bayly, an imam who publicly called for my death, was chosen to provide “religious services, leadership and guidance” at a federal prison shows that U.S. authorities haven’t learned the right lessons from a growing list of prison-convert terrorists. Bringing in radical imams to mentor vulnerable inmates will not do anyone any good—least of all prisoners looking for a better path in life.

Ms. Hirsi Ali, a fellow at the Harvard Kennedy School and the American Enterprise Institute, is the author of “Heretic: The Case for a Muslim Reformation,” just out from HarperCollins.