Twitter is working with law enforcement to investigate threats made against its executives and employees.
What appear to be ISIS supporters on Sunday called on jihadists in an online post to kill Twitter co-founder Jack Dorsey, CEO Dick Costolo and Twitter employees in general because the social network has been actively blocking ISIS-related accounts.
The post, which can be see on the justpaste.it website, and translated by Bing, says, in part, "You started this war is lost, and we told you from the beginning that it is not your war!
The online threat condemns Twitter for suspending Twitter-related accounts.
It's not clear who posted the threat but it contains the black ISIS symbol, as well as an image of a man who appears to be Dorsey in a gun's cross-hairs.
Twitter took down the original tweet and the account that posted it was suspended.
"Our security team is investigating the veracity of these threats with relevant law enforcement officials," a Twitter spokesman said in an email to Computerworld.
Twitter's own rules of service specify that users "may not publish or post direct, specific threats of violence against others."
ISIS, a terrorist group that gained notoriety around the world for capturing and beheading its victims, has been actively using social media to spread its messages, as well as to post videos of its murders.
Twitter responds to user reports of suspected ISIS accounts that threaten or support violence by shutting down those accounts.
Zeus Kerravala, an analyst with ZK Research, said Twitter is smart to delete all of the ISIS-related accounts it can find.
"Twitter has been actively trying to take down accounts that are linked to ISIS so they are impeding ISIS' ability to recruit people," he said. "When it comes to ISIS, I would consider it a very serious threat. The ISIS organization has shown it has no moral compass whatsoever... It's pretty scary stuff."