Andrew and Patricia Murray said the question and answer which lost them the chance to win $580,000 in 2011 was incorrect and was "a trick question", according to TMZ.
The Daily Mail reported the format of the now defunct Fox show, gives each pair of contestants $1million at the start of the game, and they then have to wager the money on a series of seven questions.
The Murrays answered the first five questions with $580,000 intact, and decided to bet it all on the sixth, which was, "What is the most common computer password?"
The three possible options were "Password", "123456" and "I Love You". Based on their interest in computers, the couple went for "Password", but was told the correct answer was "123456".
TV Week reported they are now suing Endemol, after they learned the answer was "based on analysis of a hacking incident involving a website known as RockYou.com".
TMZ said in the documents filed in court, the Murrays argue "If [they] would have known that the question was pertaining to a random, single incident ... they would have hedged their bets and played differently."
The Murrays are demanding the $580,000, as well as damages and expenses.
This is second time Million Dollar Money Drop has come under fire over a controversial answer.
Two contestants were denied $800,000 in winnings after they said that Post-It Notes went on sale before the Walkman, even though that is the correct answer.