CQ Politics reports that purchases by an "institutional investor" on InTrade drove up the site's odds that John McCain would be elected.

An internal investigation by the popular online market Intrade has revealed that a single investor's purchases prompted "unusual" price swings that significantly boosted the prediction that Sen. John McCain will become president.

Over the past several weeks, the investor has pushed hundreds of thousands of dollars into one of Intrade's predictive markets for the presidential election, the company said, resulting in repeated monetary losses through a strategy that belies any financial motive.

The investor doesn't appear to have violated any of InTrade's rules. But because of the investor's actions, McCain "stock" was trading higher on InTrade than on similar predictive market sites. InTrade is often more accurate than polling or punditry at predicting electoral results.

InTrade's CEO told CQ he has spoken with members of the firm that holds that institutional investment account. He declined to discuss whether the investor has political ties.