Democratic presidential nominee Hillary Clinton said that, if elected, she would try to curb terrorists from using the Internet as a recruiting tool.
"We will disrupt their efforts online to reach and radicalize young people in our country. It won't be easy or quick, but make no mistake – we will prevail," Clinton said in her acceptance speech at the Democratic National Convention.
But Clinton's statement raises questions over what can be done to prevent terrorists from using Facebook, Twitter and other social media as extremist hunting grounds.
"I believe [social networks] have been used by terrorist groups for years," said Elizabeth Boudine-Baron, an analyst with the Rand Corp., a nonprofit research organization. "I think Twitter and Facebook are major platforms being used. ... and YouTube. It can be hard to get rid of stuff, but we can make it harder for the casual observer to find so it's not the first thing popping up."
Online recruitment has been an ongoing issue in the fight against terrorism. "Twitter works as a way to sell books, as a way to promote movies, and it works as a way to crowdsource terrorism -- to sell murder," FBI director James B. Comey said in December, according to a report in the New York Times.
With the benefit of the Internet, and social media in particular, terrorists can expand their networks beyond their own borders, reaching into homes in the U.S., Europe and around the globe. The Islamic extremist group ISIS had a minimum of 46,000 Twitter accounts in the September-December quarter of 2014, according to a Brookings Institution study.
Now a teenager from small-town America can be spotted, recruited and tutored to launch an attack in his own community.
Terrorist groups, such as ISIS, Al-Qaeda or home-grown white supremacists, use social networks, including Twitter, Facebook, YouTube and the cloud-based instant messaging service Telegram to release propaganda, call for violent action, share links and video, connect people to their English-language magazines and take credit for attacks made around the world.
Terrorist groups, which often have their own IT support system of people who are both tech and social media savvy, use social networks to find others who might be susceptible to being lured into their organizations.
Using Twitter, for instance, they identify potential candidates, reach out to them and then encourage them to connect with them through private communications.
Peter Weinberger, a senior researcher at the National Consortium for the Study of Terrorism and Responses to Terrorism at the University of Maryland, said ISIS has a large organization of people who focus on using social media for recruitment.
"We know extremists are tweeting messages," he said. "They put out games, websites and magazines. This stuff is pretty slick. For someone who is vulnerable, they could get access to this and be inspired to do violence."
In a November article on the Brookings Institution website, analyst J.M. Berger noted that social media gives terrorists the advantage of volume.
By sifting through hashtags, posts and comments on Facebook, Twitter and YouTube, among others, organizations can seek out more potential recruits than ever before.
"The world continues to deal with the offline consequences of how ISIS works online, hunting among the fringes of society for those rare individuals who can be convinced to act on its behalf, wrote Berger, who studies U.S. relations with the Islamic World and wrote Jihad Joe: Americans Who Go to War in the Name of Islam.
The U.S. government and social networks have taken steps to not only pull terrorist groups off the social networks but to use social sites to supplant their violent messages.
For instance, in February, Twitter announced that it was accelerating its efforts against terrorist groups, increasing its team that reviews reports of Twitter accounts associated with violent extremism and suspending 125,000 accounts for threatening or promoting terrorist acts since the middle of 2015.
Twitter also said it was working with law enforcement on the issue.
Facebook also has suspended accounts that it finds are associated with radicalized groups.
In February, Facebook co-founder and CEO Mark Zuckerberg said at the Mobile World Congress in Barcelona that he wanted to stop terrorist groups from celebrating attacks on Facebook and to keep them from using the social network to lure in and train new recruits.
The fact that both Twitter and Facebook have been working to stop terrorists from using their networks has not been lost on ISIS. In February, ISIS made direct – and violent - threats against the CEOs of both companies.
In a video posted to Telegram titled "Flames of the Supporters," the Sons Caliphate Army, the hactivist arm of ISIS, showed photos of Zuckerberg and Twitter CEO Jack Dorsey with digitally added bullet holes.
"You announce daily that you suspend many of our accounts, and to you we say: Is that all you can do?" the hackers wrote in text across the video. "You are not in our league.... If you close one account we will take 10 in return and soon your names will be erased after we delete your sites, Allah willing, and [you] will know that we say is true."
Facebook, Twitter and Google did not respond to repeated requests for comment on terrorists' using of their sites.
YouTube, which also terminates known terrorist accounts, has a team working around the clock that reviews videos flagged as potentially objectionable. Under each video is a "promotes terrorism" flag, which viewers also can use to alert YouTube of such videos so they can be taken down.
What else can be done?
Rand's Boudine-Baron, who has been researching terrorists and their social media activities since 2014, said that while the account suspension campaigns reduce the ease with which people can stumble on to terrorist content and outreach, there needs to be a bigger presence in "counter messaging."
That's where the government and social networks could work together.
"Various government organizations are engaged in counter messaging campaigns," said Boudine-Baron. "What content can they provide to offer an alternative message? They might provide stories of people who have left ISIS and their reasons behind it; former jihadis countering violent extremism."
Using sites like Facebook, YouTube, Telegram and Twitter gets the counter messages to the same population that the terrorists are preying on.
The government, according to Boudine-Baron, could play a role in helping to find the right people to make the counter messages. A troubled teenager might not pay attention to a tweet from someone in law enforcement but might listen to someone who has suffered from terrorism or who used to be involved with a terrorist group but turned his life around.
The government, she added, also could offer financial assistance to groups and social networks working on counter messaging.
"Our government needs to figure out ways to make counter-messaging strategies more effective," Boudine-Baron said.
Weinberger agreed, saying that the focus should be on intervention campaigns.
"If there are chat rooms where people are talking, think about discrediting that message and get to these same people who are vulnerable and try to redirect them," he said. "Let's say someone says, 'Look at this hashtag.' Then you need someone else debunking that but they have to have someone who would be respected or has an authoritarian voice in that community."
Gina Ligon, an assistant professor at the University of Nebraska at Omaha, who also has been conducting research for the consortium on terrorism, said it would be useful to have more information on how terrorist groups share their messages online and what their point of influence s.
"We also need to look at what ISIS has done well and what they have struggled with so we could learn for future groups who use these tactics," Ligon told Computerworld in an email. "We have seen an increase in similar techniques from the Al-Nusrah front and other global jihad groups."
She added that the government also could fund research on the online influence of violent extremist groups -- both domestic and international.