In September, a bug was reported in Excel 2007 which makes 850×77.1 display as 100,000 instead of the correct 65,535. Many people theorized about the cause. Chris Lomont did something different: he analyzed the behavior of the code in depth, and found the problem, producing a 25-page paper with code and diagrams: An Analysis of the Excel 2007 “65535” Bug. This is an impressive piece of work, and is an instructive example of the difference between what problems appear to be, and what they actually are.

It also includes this paragraph in the conclusion:

A final comment to lawyers confused about fair-use issues, reverse-engineering for interoperability, First Amendment and DMCA issues, and the like. Be sure to do your homework before you contact me. It will save us both time and one of us embarrassment.

Chris has a lot more than that, too. His site has tons of math-meets-computers goodness, including graphics code, puzzles, screen savers, floating point tricks, LED hacking, superball pranks, and so on. Good fun.