Instructions: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: ISIS has threatened Twitter founder Jack Dorsey and his employees after the site removed accounts linked to the extremists. Twitter confirmed to Daily Mail Online that the company was working with authorities to verify the seriousness of the threat which claimed employees' necks are 'a target for the soldiers of the Caliphate'. The chilling warning, written in Arabic, featured a picture of Dorsey in a gun's cross-hairs and the Twitter logo. It was posted on Sunday on an anonymous site based in Poland which is used by programmers to share code. Dorsey, who is worth an estimated $2.5billion and lives in California, made no mention of the threat online on Sunday as he tweeted his 2.87million followers.Twitter confirmed to Daily Mail Online on Monday that the company was working with authorities to verify the seriousness of the threatThe threat, featuring a picture of Dorsey in a gun's cross-hairs and the Twitter logo, was posted on Sunday 
 Question:According to _'s rules: 'You may not publish or post direct, specific threats of violence against others.'
Output:
Twitter