The details are over on DailyKos, but here is a summary.
Hillary Clinton put out a campaign ad where a picture of Barack Obama was used. The photo was altered to make his skin darker. If that wasn't bad enough, the ratio was also altered, or "squished", to make it seem as if he has a wide, flat nose.
In this ad, she also lies about his subcommittee, saying it's responsible for Afghanistan, and that he hasn't held hearings. Problem is, Afghanistan is under another committee.
Then, when confronted, the Clinton campaign denies that the ad is theirs. Except the ad was on Clinton's own site. Oops.
Seriously, go read this, look at the facts. This is absolutely horrible behavior. This woman does not deserve to be president, by any stretch of the imagination.