Violent jihadists of the Islamic State in Iraq and the Levant (Isil) have been able to count on as many as 45,000 Twitter users to spread their message, according to a new survey of social media.
They include thousands of "bots" - automated computer tweeters - and are flourishing despite frequent suspensions.
The findings were presented to Congress on Tuesday by JM Berger, a fellow of the Brookings Institution and an expert on the use of social media by jihadist groups.
He said there was nothing mysterious about how Isil was exploiting social networks to spread its message and that it was vital to target its most active users.
"These accounts - described fully in data collected over the last two years as well as in Isil strategy documents - act in a co-ordinated way to amplify Isil's message, tweeting links to Isil propaganda and hashtags at an unnaturally fast pace, which causes them place higher in search results and results in content being aggregated by third parties," concluded the report.
The full findings will be released in March, but provide a snapshot of online jihadist activity in the autumn as part of a study to investigate the impact of Twitter's policy of suspending suspect accounts. It comes at a time when governments are grappling with how best to police social networks while opponents fear the erosion of internet freedom.
"In addition, Isil and more recently, al-Qaeda in the Arabian Peninsula, use 'bots', computer-controlled Twitter accounts that automatically send out content in a similar manner," said Mr Berger in his evidence to the House Committee on Foreign Affairs, which is investigating terrorist propaganda in the wake of the Charlie Hebdo attack.
"Thousands of such bots support ISIS and other illegal ventures."
His report said Twitter had begun targeting Isil accounts more actively shortly before the group released a video showing the murder of James Foley, the American journalist.
Some 800 confirmed Isil users - and another 18,000 related ones - had been suspended since the autumn, drawn largely from the busiest and most-followed accounts.
Last year, ShamiWitness, one of Isil's most high-profile social media supporters was arrested by Indian police after being unmasked as a worker from Bangalore.
"If suspensions do not continue at a consistent pace and with consistent criteria, the targeted network will regenerate," the report warns. "The suspension process is akin to weeding a garden. You don't 'defeat' weeds, you manage them, and if you stop weeding, they will grow back."
But there are benefits in leaving some users alone, said the report: "By allowing some Isil accounts to continue with a lower profile, the current level of suspension activity preserves a substantial amount of open-source intelligence."