Don't enter your personal information into random websites.
This includes random websites that ask your credit card info. (hopefully that's obvious.)
This includes random websites that ask your LiveJournal password (unless you trust those sites not to slurp all your private posts out of LJ). (yes, this is part of why you'd better not use your Facebook password on any other site, ever, since all Facebook is *ABOUT* is blasting your Facebook details to every tom-dick-and-harry who wrote a Facebook "I JUST THREW WOODY ALLEN AT YOU LOL" plugin.
...And this includes websites that purport to check your voter registration status.
The Colorado site for it is here: http://www.sos.state.co.us/Voter/voterHome.do
Or, start at the state government homepage ( www.state.co.us or www.colorado.gov ) , mouseover 'How do I', choose 'Register to vote', and click 'Verify Your Voter Registration Information')
Don't use "Mallory's Voter Checker and LolCat Caption Generator". You don't know what Mallory's doing with the data you just provided.