The FBI says it has 1,000 open cases on radical Islamic extremists operating in all 50 states.
According to the FBI's director Christopher Wray, countering the threat posed by these suspected or potential terrorists is now the agency's top priority.
During congressional testimony last week, lawmakers like Sen. Susan Collins of (R-Maine), wanted to know how the bureau was handling the danger from homegrown extremists, many of whom are inspired by or radicalized over the internet by Al Qaeda, ISIS, and other Islamic terror groups.
"How is the FBI countering that threat?" asked Collins. "It seems to be very difficult to identify these individuals."
"You are exactly right," Mr. Wray told Sen. Collins. "You've put your finger on what I would sort of say is our highest counterterrorism priority at the moment."
"We have about a thousand investigations into exactly the kind of people you are describing, covering all 50 states," Wray told the Collins.
Despite its losses on the battlefields of Syria and Iraq, Wray warns ISIS and other Islamic terror groups remain a series threat to the homeland.
"The good news is the caliphate is crumbling, and that's positive for all of us," Wray said during a House Judiciary Committee oversight hearing in December 2017. "The bad news is, ISIS is encouraging some of its recruits and potential recruits to stay where they are and commit attacks right in the homeland."
Wray says those open cases does not even include the bureau's ongoing investigations into Al Qaeda, ISIS, and other domestic terrorism threats.
"What makes it so hard is that there aren't many dots connecting some of these people," Wray said. "They pick soft targets, they use easy to use weapons like IED's, cars, knives, guns and they can make decisions on the spur of the moment."
Security experts say keeping track of so-called "lone wolf" attackers is not always easy.
"We are trying to get better at looking for red flags as to when people are getting radicalized and start to make that switch into potentially mobilizing," Wray told lawmakers.
This isn't just an American problem. Across Europe, Africa, Asia and parts of Middle East, various governments are also dealing with the threat from Muslim radicalization.
"This is something I compare notes with my foreign counterparts on a lot and they have the same challenge, all of our closest allies have the same issue," Wray warned during his testimony.
In April, ISIS released an audio recording urging followers to launch attacks against Arab nations. Security experts say terrorists are constantly changing their tactics to avoid getting caught.
"We face ambitious adversaries who are continuously looking for a point of attack and waiting for us to slip up," David Pekosk, head of the Transportation Security Administration (TSA), said recently.
Pekosk says the TSA is likewise adjusting its tactics to counter a rapidly changing threat matrix.
"Today we are confronted by a current of less-sophisticated techniques and tactics, where lone wolves, radicalized on the Internet, are using inexpensive, low-tech methods to target civilians," Pekosk said.
On the heels of last weekend's deadly lone wolf terror attacks in France and Indonesia, terrorism experts say its vitally important that the U.S. develop effective strategies to counter the constantly evolving threat posed by lone wolf attackers.
"The possibility that a terrorist group or individual could gain access to WMD or the means to trigger a widespread cyber attack that cripples our major financial systems and critical infrastructure continues to be a major concern," said Carol Rollie Flynn, the former top official at the CIA's National Counterterrorism Center. "
"Preventing these types of attacks is very, very hard because the tools of law enforcement... to detect and pre-empt attacks don't work if the terrorist is not connected in any detectable way to a known terrorist or terrorist group," Rollie added.
On Tuesday, millions of Muslims around the world started their annual 30 days of fasting and prayer during Ramadan.
"Ramadan is a month of receiving divine blessings and abstaining from food and drink," said Mohammad Linkon Mollah, a Muslim university student in Bangladesh.
While the majority of Muslims use the time to grow closer to Allah, terror experts say there's a growing number of Islamic jihadists who also use the month "to engage in acts of violence in the name of Islam."
"Jihadists see Ramadan as an especially auspicious time for attacks, believing that actions taken during Ramadan are somehow nobler, and despite prohibitions on aggression of any kind during the month," said Stratfor, the intelligence group that monitors Islamic threats worldwide. "The Islamic State, al Qaeda and other jihadist groups have all sought to foment attacks during Ramadan with promises of greater rewards in the afterlife."
Stratfor anticipates "an increase in the tempo and intensity of attacks, a trend continuing from the previous two years."
According to SITE Intelligence Group, which tracks terrorist groups online, ISIS claimed responsibility for 300 attacks during Ramadan last year, including last year's attack on a bus of Coptic Christians in Egypt.
That's why one group is urging Christians to also use the month of Ramadan to pray for Muslims.
The international movement known as "30 Days of Prayer for the Muslim World" began in 1993 and calls the global Church to make a focused effort to learn about, pray, and reach out to Muslim neighbors.
"While media sound bites about Islamic extremism can too easily incite anger, fear and even hatred towards Muslims, we seek to resist this temptation to generalize, and instead, resolve to respond and pray with the mind and heart of Christ," reads the prayer website.
Meanwhile, Open Doors USA, a group that documents atrocities against religious minorities, is calling for prayer for Christians who live in Muslim-majority countries.
"While here in the US the holiday is beginning to gain mainstream recognition...in other parts of the world it is so widely celebrated, the few who do not adhere to its traditions become the obvious outliers as they don't participate in the fasting or calls to prayer," Open Doors states. "In fact, Christians in predominantly Muslim countries often experience increased persecution during this time."