In this series, we take a look at the 25 stocks on the S&P 500 Index (SPX) that have turned in the worst performance during the past decade -- what went wrong, and what happens next.

New York-based Interpublic Group of Companies (NYSE: IPG) is a marketing services firm, but they're not your average PR hucksters. Flip through IPG's resume, and you'll find that they were once tapped as the "brand steward" for Coca-Cola Classic. Is there a more solemn task in the world of marketing? Perhaps -- Coke also handed IPG the reins on Cherry Coke, but jealously guarded its Sprite brand from the mega-marketer's grasp.

What went wrong? At number 22 on our list of SPX underperformers, IPG lost 72% of its value from June 30, 1998 through June 30, 2008. The worst of the stock's woes occurred during the first several years after the turn of the millennium. A broad economic slowdown led many clients to trim their spending on advertising, and -- as one of four "megacompanies" that essentially ruled Madison Avenue -- IPG couldn't help but feel the pinch.

Even as the marketing behemoth faced down this fundamental challenge, an accounting fiasco caused the company to restate six years' worth of financial results. Interpublic soon found itself facing a formal investigation by the Securities and Exchange Commission, along with an IRS audit over the small matter of $41.5 million in unpaid taxes.