This was breaking news on the Fox News Twitter account earlier today.
It's untrue and the account had been hacked.
Hackers tweet ‘Obama assassinated’ on Fox News account
A group of hackers targeted a Fox News Twitter account early Monday morning and posted a series of false updates declaring that President Barack Obama had been assassinated.
It is reported that the hackers behind the Twitter attack have now claimed responsibility.
‘Scriptkiddies’ took control of [at]foxnewspolitics - a bona fide account of the US news service with 33,000 people following it - at the beginning of 4 July, which is a public holiday in the US for Independence Day.
People following Fox’s politics feed account would have seen the shocking hoax posts that claimed the President was dead appearing from 2.43am EDT (Eastern Daylight Time), with hundreds of them forwarding this on to their followers.
Hackers tweet