As the Democratic primary draws near to the Iowa Caucus, the sparks -- and sleaze -- are starting to fly.

The latest mud: columnist Robert Novak reported Friday that "agents of Sen. Hillary Clinton are spreading the word in Democratic circles that she has scandalous information" about Sen. Barack Obama.

So what dirt does Hillary have about the Illinois Senator?

Novak says the details, so far, have not been disclosed.

Democratic primary campaigns can be particularly dirty. Remember Sen. Gary Hart's "Monkey Business" affair that was reportedly dredged up by operatives of his 1988 primary rival Al Gore.

Also remember the Gennifer Flowers scandal. Republicans get blamed for the "Clinton Hate Machine" -- but the truth is that the buzz against Bill Clinton was fed by Democratic operatives in the '92 primary campaign.

This time, Obama is on the offensive and quickly lashed out at Hillary.

In a statement released by his campaign this weekend, Obama said: “The cause of change in this country will not be deterred or sidetracked by the old ‘Swift boat’ politics. The cause of moving America forward demands that we defeat it ....

“I am prepared to stand up to that kind of politics, whether it's deployed by candidates in our party, in the other party or by any third party."

Obama demanded that Hillary and her operatives release their "scandal" or deny they are part of an effort to smear him.

An angry Obama added, “She of all people, having complained so often about ‘the politics of personal destruction,’ should move quickly to either stand by or renounce these tactics.”

Clinton's campaign hurriedly responded to the growing brouhaha. Clinton spokesman Jay Carson told Fox News that the campaign has "absolutely no idea what [Novak] is talking about. ..."

Carson said, bluntly, Hillary Clinton's campaign had no scandalous information about Senator Obama.

Word of the Obama scandal comes as Hillary has lost her momentum after flip-flopping on the issue of licenses for illegals. Obama appears to be gaining, and recent polls in Iowa show him closing the gap with Hillary.