As reported earlier, Indiana officials are investigating possible forged signatures in the 2008 petitions to place Barack Obama, and also Hillary Clinton, on the Indiana presidential primary ballot in 2008. Now the McCain petition is also being investigated, with some preliminary reason to believe that petition was also invalid. See this story.
Indiana requires more signatures than any other state for candidates who are discussed in the media to get on the ballot in a presidential primary, except Virginia requires even more. Indiana requires 4,500, and there must be at least 500 from each U.S. House district in the state. Thanks to Rick Hasen for the link.