This has been known for decades, but still a good article for those who don’t already know it, from Fox News.

An excerpt.

America’s federal prisons have become a “breeding ground” for radical Islam, warn critics, who say imprisoned terrorists are more likely to spread their beliefs than renounce them.

As law enforcement authorities lock up more home-grown terrorists, experts are warning the success could turn sour if jailhouse jihadists are allowed to infect fellow inmates. Prisons have long been criticized for a culture that can make some inmates more dangerous than when they entered, but the possibility that typical felons could become lone wolf terrorists upon earning parole is a disturbing new wrinkle.

“If we continue to downplay the threat, we do so at our own peril,” said Patrick Dunleavy, author of “The Fertile Soil of Jihad: Terrorism’s Prison Connection.”

The aggressive recruitment of Americans by ISIS has resulted in a spike in domestic terror-related convictions. Some 71 people are imprisoned in the U.S. on ISIS-related charges, including 56 individuals arrested in 2015, the most terrorism arrests in a single year since September 2001, according to George Washington University’s Program on Extremism.

In addition, the FBI has said it is currently conducting more than 900 investigations into ISIS-linked radicalization, including cases in all 50 states.

There are hundreds more federal inmates serving time for terrorist activities related to other terror groups. An estimated 100 are scheduled for release in the next five years, according to the Congressional Research Service. Still more terror suspects could be transferred to U.S. prisons from Guantanamo Bay in the coming months.