At first I thought this was some sort of homeland security issue, but it turns out to be nothing like that at all. Apparently people have been running for judicial office in Cook County under Irish names because they think they can get more votes that way.
In 2005, a man named Frederick Rhine changed his name to Patrick O'Brien in preparation for his campaign for judge the next year. In the end he didn't even run, but a state representative, John Fritchey, decided this was a serious problem, introduced a bill to stop it, and moved the thing all the way through both houses and got it signed by the governor.
So if I decide to run for the Illinois legislature in 2008 under the name Paddy O'Rourke, the ballot will have to include the words "formerly known as Alan Ehrenhalt." That's not so good. But there is the three-year loophole. Somebody could change his name to Richard R. Daley, wait out the time period, and run for mayor in 2011 without disclosing anything. I wonder if this law might end up encouraging more mischief than it prevents.