I remember hearing about huge investments the IRS made into technology to catch tax evasion, and the controversy it caused at the time.

This article from the Intercept on the front page reminded me of the IRS implications of this

Here's another article: http://money.usnews.com/money/personal-finance/mutual-funds/articles/2013/04/12/what-does-the-irs-know-about-you

"The Internal Revenue Service says it will not snoop online to see if you are evading taxes—unless your tax return signals something suspicious.

Once you are flagged, however, the IRS can draw on massive amounts of personal data it routinely compiles on peoples' electronic activities—everything from credit card transactions to Facebook postings. Most recently, the American Civil Liberties Union says it has IRS documents that reveal the IRS believes it has the legal authority even to open private emails without people's knowledge and sometimes without a warrant."