The tweets were posted between 2 a.m. and 3 a.m. Eastern Time by the "foxnewspolitics" account. The account has a badge with a checkmark that means it has been verified by Twitter for authenticity.
National media outlets in the U.S., including Fox News itself, carried no such reports. Fox News ran a story on its website acknowledging the hack, saying it "regrets any distress the false tweets may have created." The false tweets came on a major U.S. holiday, Independence Day.
The first tweet about the assassination -- addressed directly to Obama's real account -- said "@BarackObama has just passed. The President is dead. A sad 4th of July, indeed. President Barack Obama is dead."
Subsequent tweets said that Obama had been shot twice in the lower pelvic area and the neck and that he later died from his wounds, with the shooter unknown.
Earlier on Monday morning, the Huffington Post reported that the Fox News Politics Twitter feed had been hacked. A screenshot posted by the Huffington Post, showed the Fox News Politics feed carrying the subtitle: "H4CK3D BY TH3 5CR1PT K1DD3S." The channel's logo had been replaced with the capital letters SK, presumably also a reference to script kiddies, a term applied to youths who hack computers using simple, automated tools or scripts developed by others.
The screenshot also captured two other messages, subsequently deleted, on the Fox News Politics feed, one taking credit for the hack and another directed at Anonymous, the hacking collective that has led a highly successful hacking campaign. That tweet also referred to "antisec," short for "Anti-Security," an ongoing hacking operation conducted by Anonymous that has antagonized companies and governments by defacing websites and, in some cases, stealing sensitive data.
The first in the series of strange tweets still visible on the account said that the account owners had regained full access to e-mail and the Twitter feed, in an attempt to allay suspicion about the earlier, now deleted, messages.
Twitter typically moves quickly to delete tweets that come from hacked accounts and has overall stepped up its security. But like many web-based services, Twitter uses logins and passwords to allow access to accounts, which hackers have proved adept at stealing through social engineering techniques and malware on computer such as keyloggers.
Officials at Twitter, which is based in San Francisco, Calif., said they do not comment on specific accounts for privacy reasons but added that users should follow its strong password advice.
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