SAN FRANCISCO, Calif. (KTVU) -- Twitter co-founder Jack Dorsey and employees at Twitter's headquarters in San Francisco have become the targets of online death threats allegedly posted by supporters of ISIS.
Twitter issued a response to an online message that included death threats and calls for ISIS supporters to target Twitter buildings, employees, and Dempsey, who also serves as the social media company's Board Chairman.
The message surfaced on the website Pastebin Sunday, but it was unclear who posted the message. An online photo also showed Twitter chairman and co-founder Jack Dorsey in cross-hairs with the Twitter logo.
The message appears to be in retaliation for Twitter's removal of accounts related to the terrorist group, the Islamic State of Iraq and Syria (ISIS) which is fighting to take over parts of Syria and Iraq. ISIS has been taking its war online, using social media as a central part of it's strategy to recruit members worldwide and distribute videos of ISIS fighters and hostage deaths.
A Twitter spokesman responded to KTVU Monday with a statement.
"Our security team is investigating the veracity of these threats with relevant law enforcement officials," said Twitter spokesman Jim Prosser.
At Twitter headquarters in San Francisco, everything appeared quiet Monday evening. Some employees told us off camera they had not received any company notices about security.
People who work in the same building as Twitter say security is tight.
"It didn't surprise me, because I think in the past there have also been threats," said Xian Ke, co-founder of Pomello which has offices in the same building as Twitter.
"I know just compared to other office buildings I'm in, this building is already more secure," Ke told KTVU.
Outside, a guard told us there was additional security posted around the building.
In the past few days, Twitter reportedly has suspended ISIS accounts, finding at least 2,000 accounts linked to ISIS and its supporters.
Twitter's rules for users clearly states: "You may not publish or post direct, specific threats of violence against others." The website says accounts may be terminated for violation of the rules.
Monitoring postings by terrorist groups has become part of a growing challenge for social media companies including YouTube, which also has been used by terror groups to recruit and post videos.