Excel and other spreadsheets aren't intrinsically evil, but like any power tool, they can easily take off fingers when used carelessly. From Neil Saunders' blog:
...a text download of 450K methylation from the Cancer Genome Atlas project reveals that Excel has had its evil way with the data at some point. Gene names such as MAR1, DEC1, OCT4 and SEPT9 are now reformatted as dates.
As he goes on to say, "Despair at the quality of public data, fears about reproducibility in science. Must be Monday."