Al-Qaeda and other terrorist groups have expanded their online presence with increased use of social media, creating new challenges for thwarting attacks, said a study released Wednesday.

The study released by the Woodrow Wilson Center's DC Commons Lab found terrorist groups have moved their online presence to outlets such as YouTube, Twitter, Facebook and Instagram.

"All terrorist organizations are online using many platforms," said Gabriel Weimann, a University of Haifa professor of communication and author of the report.

"From the point of view of a terrorist, (social media) provides an important advantage: anonymity," Weimann told a forum at the Wilson Center where the study was released.

Weimann said these social media have become important tools for recruitment, propaganda, fundraising and even for training -- such as how to build a bomb.

Weimann, who has been studying communications of terrorists for years, said that in 1998 only 12 terrorist-related websites were in existence, and now the figure has grown to nearly 10,000 plus related social media presence.

"They have launched forums and chatrooms. They added social media," he said.

Weiman said the groups "never invented anything" online but have taken advantage of online freedom to create tools such as the slick online English-language magazine "Inspire" used to recruit and train sympathizers in the United States and elsewhere.

- Targeting the young -

Social media allow terrorist groups to take a more proactive role in reaching people, and can connect more easily with a younger audience.

"Terrorists have good reasons to use social media," he says in the study.

"First, these channels are by far the most popular with their intended audience, which allows terrorist organizations to be part of the mainstream. Second, social media channels are user-friendly, reliable, and free. Finally, social networking allows terrorists to reach out to their target audiences and virtually 'knock on their doors' -- in contrast to older models of websites in which terrorists had to wait for visitors to come to them."

Weimann said the social media enables groups to keep alive some of their heroes, like Yemeni-American cleric Anwar al-Awlaki, who was killed in a US drone attack after being targeted by Washington for fomenting terror attacks.

YouTube has simplified sharing for terror organizations of videos, including those of assassinations and kidnappings, the report said.

And Twitter has become a way for groups to "live tweet" actions, such as last year's deadly attack on the Westgate shopping mall in Kenya, Weimann added.

Weimann argued that trying to block terrorists' online activity is mainly counterproductive, and that it may be more useful to monitor and learn from their online activities.

"There is no way to block them," he said.

The Al Qaeda linked group Al-Shebab was removed from Twitter after the Westgate attack, he noted, "but they were back up in a few days."

Weimann said the growing online presence of terrorists underscores the need for improving surveillance, such as systems used by the National Security Agency, but with safeguard to protect privacy.

"There is a crucial need for monitoring" or terrorists online, he said, "but all of this must be regulated."