This has been a banner year for US law enforcement's battle against "terrorism".

As of right now, US authorities have arrested 56 people in 2015 on charges related to their attempts to join or aid the Islamic State of Iraq and the Levant (ISIL) group, according to a new report from George Washington University.

It's the most terrorism-related arrests in a single year since the 9/11 attacks on the US.

Why the high number?

"I think US prosecutors have gotten a bit creative on their charges in some cases," said Seamus Hughes, a former counterterrorism official with the US government and co-author of the report.

"I think there's a realisation and a concern on law enforcement's part to rightly try to prevent the next attack."

But ISIL's online efforts have also been a big contributor to the uptick in arrests.

"I think their use of social media has attracted more people than it has in the past," said Hughes.

Indeed, the majority of the people charged with aiding ISIL were between the ages of 18-26 years old, according to the report, a key demographic when it comes to social media. ISIL is particularly active on Twitter, the report found.

According to Ambassador Alberto Fernandez, a former state department official who specialises in ISIL's social media presence, the group produced 1,800 videos in the past year, 14,523 graphics, worked in nine languages and created 50 songs.

Much of the message to Westerners is positive and less religious than its Arabic output. "The material in English is more superficial," said Fernandez. "It's fervent, incessant, but shallow."

The report also found that 86 percent of the Americans who join ISIL are male and 40 percent of them are converts to the Muslim faith. Their motives vary.

Roughly half of those charged with an offence attempted to travel abroad or successfully left the US before they were caught, according to the report.

Although there were ISIL-related arrests in 21 states, New York and Minnesota had the highest numbers.

Source: Al Jazeera