A long time ago, when it was still a fairly common and feasible practice to put an entire app's database on a few floppy disks, I made the mistake of fiddling with the .DBF files without first making a backup. Needless to say, I screwed something up and had to spend the rest of my weekend fixing the files using a C program I cobbled together to gather up all the old data into new tables. Luckily, I had enough information from reference materials on hand to be able to figure out the file format and where all the data was on the disks (this pre-Internet times). Still wasn't fun and my supervisor rightfully chewed me out for not taking proper precautions.