I recall opening a csv of user data in excel, and one particular user had a username of april0204 (can't recall the actual number but you get the idea). It took me a moment longer than I care to admit to realize what had happened as i stared at the random date in the middle of my username column
A while ago I got some Excel CSV exports that I couldn't read as I normally do. I tried several formats that I knew were associated with Windows systems. I ended up looking at the raw bytes and I noticed that every other byte was something like 0x00, so I wrote a script to strip all of that out. Several weeks later I figured out that I had been looking at utf-16. Derp.
