Around 12 p.m. ET Monday, the verified Burger King Twitter account was changed to a McDonalds name and logo with a Fish McBites background image. The account's description was edited to read "Just got sold to McDonalds because the whopper flopped."
It's unclear who is behind the hack.
"We're guessing the @BurgerKing social media team is having a bad day," said a post from hacker legion Anonymous, re-Tweeted from the hacked Burger King account.
Burger King fans alerted the fast food chain to the hack on its Facebook page, but Burger King has not yet responded.