ISIS supporters operated at least 46,000 Twitter accounts, study finds

The accounts were in use between September and December, and while not all were active at the same time, the estimate is a conservative one. The actual number could be as high as 70,000, according to the study, which was commissioned by Google Ideas and published by the Brookings Institution, a Washington, D.C., think tank.

The report, one of the biggest of its kind, sought to investigate not only the scale of ISIS' presence on social media but also to provide a "demographic snapshot" of its supporters and their methods.

Much of its activity on Twitter can be attributed to a group of 500 to 2,000 hyperactive accounts that sent tweets in concentrated bursts. The accounts supportive of ISIS had an average of 1,000 followers each, the study found, many more than most ordinary Twitter users.

The report's authors recommended that social media companies and the U.S. government work together to devise a response to extremism on social media. While government intervention might be seen as a violation of free speech, it says, "in reality, social media companies currently regulate speech on their platforms without oversight."

The report comes as Twitter is stepping up its efforts to deal with all types of abuse on its network.

It suspended at least 1,000 accounts supportive of ISIS during the last four months of 2014, the study says. A recent ABC News report says Twitter suspended 2,000 ISIS accounts last week alone.

Meanwhile, supporters of ISIS have threatened Twitter's CEO, its cofounder and other employees over the company's efforts to block ISIS-related accounts.

The content posted has sometimes been graphic and violent. ISIS, also known as the Islamic State of Iraq and Syria, has published images and video of journalists and others being beheaded, and of a Jordanian air force pilot being burned alive. Some of its videos are posted to Google's YouTube service as well.

Asked to comment on the report, Twitter said: "We review all reported content against our rules, which prohibit unlawful use and direct, specific threats of violence against others."

ISIS accounts that tweeted the most often and had the most followers were more likely to be suspended, the report's authors wrote. They based their findings on an analysis of 20,000 Twitter accounts supportive of ISIS.

Not surprisingly, its supporters were typically located within the organization's territories in Syria and Iraq, as well as in regions contested by ISIS, the report said.

The report's lead authors were J.M. Berger, a nonresident fellow at Brookings, and Jonathan Morgan, a data scientist who runs technology and product development at CrisisNET, a repository of world crisis data.

Zach Miners covers social networking, search and general technology news for IDG News Service. Follow Zach on Twitter at @zachminers. Zach's e-mail address is zach_miners@idg.com