Timothy Geithner is one of 42 million Americans who prepare their own taxes online - and now he might be the most popular. Except in the case of Geithner, the Treasury Secretary-designate, it seems he didn’t follow the directions.

At his confirmation hearing Wednesday, Geithner admitted to more than $40,000 worth of mistakes on his tax returns from 2001 to 2004 while he worked for the International Monetary Fund. Geithner says it was an innocent mistake.

When Senator Chuck Grassley asked him what program he used to prepare his taxes, he answered, “I’ll answer that question, but I will say these are my responsibilities, not the tax software’s responsibilities, but I used TurboTax to prepare my returns.”

The chamber crowd laughed in response.

TurboTax is the popular software sold by Intuit (INTU), the business and financial management company that also sells Quicken and Quickbooks. Intuit is the clear market leader in do-it-yourself tax-preparation. Although Intuit may not have found Geithner’s admission funny, well, any press is good press.

Intuit sold about 6.5 million copies of its boxed TurboTax software last year, which is about 80% of the market for federal tax return software, according to the company. H&R Block (HRB), Intuit’s main rival, owns the other 20% with its TaxCut programs.

Intuit was founded in 1983. TurboTax followed 10 years later when it acquired the program’s creator, Chipsoft. With TurboTax, the company offers a product that appears to be recession-proof. Even in hard times, the IRS is merciless and impatient: You can’t postpone filing tax returns and if you've lost your job, the agency still demands you pay your taxes on time. In a recession, too, people seem more likely to prepare their own taxes rather than pay a preparer.

Because the tax code changes yearly, users of TurboTax must buy new software to keep up, providing a steady revenue stream for Intuit. The tax code now runs more than 60,000 pages; about 500 changes were enacted last year alone.

Intuit is in an enviable position as the industry leader in a stable and growing market. Users of TurboTax have stayed with the software because it's easy to use and ensures year-over-year consistency in their filings. Indeed, with Intuit’s stock trading near its 52-week low, this seems like a situation where a solid company has been tossed out with the bathwater.