The terrorist group also known as the Islamic State and ISIL recruits people from all over the world, including the US. Thousands of people from Western countries are thought to have joined the group's ranks in Iraq and Syria, where ISIS has forcefully established a self-declared Islamic "caliphate."
But for many Westerners, the radicalization process starts online, where it's not difficult to find ISIS supporters who pull people in to extremist ideology.
In its report, the Center for Cyber and Homeland Security at George Washington University said that the US "is home to a small but active cadre of individuals infatuated with ISIS's ideology," some of whom have decided to leave their homes to travel to ISIS territory or mount attacks on the homefront.
Days after the release of the report, two individuals with reported inspiration from the group carried out an attack that left 14 people dead in San Bernardino, California. Tashfeen Malik, one of the shooters involved in the attack, reportedly pledge allegiance to ISIS' leader as the incident was unfolding.
But the center discovered that there isn't one common profile for the American ISIS sympathizer - the individuals the report studied varied widely in race, age, social class, education, and family background, and their motivations "are equally diverse and defy easy analysis," according to the report.
Though there are vast differences between many of those who embrace ISIS ideology, the National Counterterrorism Center observed that "disenfranchised individuals seeking ideological, religious, and personal fulfillment" tend to be more susceptible to radicalization.
The Center for Cyber and Homeland Security report emphasized how dangerous this community of English-speaking ISIS supporters online can be to Americans. Some ISIS supporters seek out potential recruits online who haven't yet adopted radical views but might be curious about Islam.
"Our researchers observed real-time cases of recently converted Americans pulled into the ISIS echo chamber," the report said.
"In one case the seemingly naïve individual posted general questions about religion, to which ISIS supporters quickly responded in a calm and authoritative manner," it continued. "After a few weeks, the accounts of hardened ISIS supporters slowly introduced increasingly ardent views into the conversation. The new recruit was then invited to continue the conversion privately, often via Twitter's Direct Message feature or on other private messaging platforms such as Surespot."
In Senate testimony earlier this year, FBI Director James Comey noted the danger newly radicalized Americans could pose to US national security.
"ISIL blends traditional media platforms, glossy photos, in-depth articles, and social media campaigns that can go viral in a matter of seconds," he said.
"No matter the format, the message of radicalization spreads faster than we imagined just a few years ago. ... With the widespread horizontal distribution of social media, terrorists can identify vulnerable individuals of all ages in the United States - spot, assess, recruit, and radicalize - either to travel or to conduct a homeland attack. The foreign terrorist now has direct access into the United States like never before."
We've examined some of the social-media profiles thought to be affiliated with American ISIS supporters included in the report. It's hard to tell how many of these accounts belong to people with actual connections inside the terrorist organization, but these profiles nevertheless provide insight into those who are attracted to ISIS and its radical brand of Islam.
Al-Amriki
The true identity of the person behind social media accounts with the username "Al-Amriki" isn't known, but the person claims to be a 19-year-old woman and the username suggests the person is American. The Center for Cyber and Homeland Security included a screenshot of Al-Amriki's Tumblr page in its report.
Al-Amriki's Tumblr is filled with the types of interactions you'd expect to see on any young woman's social media page - she posts pop-culture memes and questionnaires in which she answers questions about her life, speaking about her sadness and isolation.
This post looks pretty typical for a teenager - until the question about her "current obsession," to which Al-Amriki answers, "sniper training":
Screenshot/Tumblr
In this post, she answers a question about whether she supports ISIS with a meme from a rap song:
Screenshot/Tumblr
And while she's careful not to admit support for any terrorist group, it's clear that she has embraced an extreme Islamist ideology.
Her Twitter page is full of violent imagery, some showing ISIS propaganda. US currency is visible in one of the photos:
Screenshot/Tumblr
Screenshot/Tumblr
Screenshot/Tumblr
On a page of her Tumblr blog where she answers questions from people who write to her, Al-Amriki has said that she is a convert to Islam. When asked, she did not specify where she lives.
Ariel Bradley
More is known about Ariel Bradley, a woman in her mid-2os from Tennessee who maintains several online profiles and last year traveled to Syria to join ISIS.
BuzzFeed News profiled Bradley earlier this year, describing how she became radicalized and left her home for life as an ISIS bride.
Bradley was raised as a Christian, but she was a rebellious teenager - at one point running away from home - and her friends said she always seemed a bit lost, wandering in search of an identity and sense of belonging. Bradley adopted new identities frequently - one female friend said: "When I first met her she was a Christian, and then she was a socialist, and then she was an atheist, and then a Muslim."
She seemed to latch on to the identity of whichever man she was dating. Those close to her told BuzzFeed that Bradley defined herself through relationships and was "always looking for love."
She thought she found it in a young Syrian student she worked with at a pizza parlor and deli near the University of Tennessee at Chattanooga.
The unnamed man reportedly didn't return Bradley's affections. He said he told her he didn't want to take their relationship any further than friendship, and Bradley seemed to think it was because she was not a Muslim and he was. After he rejected her, she started researching Islam. She converted in 2011.
Eventually, she started looking for a Muslim man to marry. She met a younger man on a Muslim dating site and married him after a few months of chatting online. Bradley moved to Sweden, where he lived, and after she gave birth to their first child they left for Syria.
Her social-media profiles say Bradley is now in Al Bab, Syria, an area under ISIS control.
She posts photos on her Instagram account, which was referenced in the BuzzFeed article and the Center for Cyber and Homeland Security report.
One shows food:
Screenshot/Instagram
Others show outdoor scenes:
Screenshot/Instagram
Screenshot/Instagram
And this one shows a Quran:
Screenshot/Instagram
Abu Asma al-Amriki
The Twitter account with the nom de guerre Abu Asma al-Amriki is also referenced in the Center for Cyber and Homeland Security report.
Little is known about the identity of this person, but he is very active on Twitter and has several backup accounts to use if Twitter suspends any of the others.
Abu Asma appears to be what the report refers to as a "node" - a creator of primary content that can be a leading voice in the online community of ISIS extremists. Groups or small clusters of these users "will often swap comedic memes, news articles, and official ISIS tweets, allowing them to pool followers and more easily spread content both to new audiences and throughout their network," according to the report.
One account Abu Asma follows, with the nom de guerre Khadijah Adam, tweeted a meme that shows how those in the online community of ISIS supporters can take the same sort of tone as teenagers on Facebook:
Screenshot/Twitter
These pro-ISIS accounts often emphasize the importance of their activity, seeming to suggest that one does not have to be a fighter to participate in radical jihad.
One tweet in particular from Abu Asma illustrates this:
Screenshot/Twitter
He then sent out a string of tweets decrying the "Western media" and calling on others to spread his message:
Screenshot/Twitter
Screenshot/Twitter
Screenshot/Twitter
Denouncing the Western media is a common tactic of radical Islamist recruiters. They look to sew doubt about the terrorist atrocities on which Western news outlets report, convincing potential recruits that these reports are not an accurate representation of ISIS.
This tactic was apparent in the radicalization process of a young American woman in Seattle named Alex, as reported by The New York Times earlier this year.
When her grandmother confronted the ISIS-linked recruiter who had been spending hours communicating with Alex online, he said: "I understand you may consider us being radical Muslims whatever that maybe? Well please don't believe everything on fox news!!"