Tax Administration: Many Taxpayers Rely on Tax Software and IRS Needs to Assess Associated Risks
http://www.gao.gov/new.items/d09297.pdf
Taxpayers used commercial software to prepare over 39 million tax returns in 2007. This report looks at how pricing of tax software influences use, the extent to which the Internal Revenue Service exercises oversight of the software industry, and the risks to tax administration from using tax software. From the Government Accountability Office