My first programming gig was reverse engineering a file format for my dad's school (he was a chemistry teacher doubling up as school admin). The person previously in charge of that position had installed a time bomb that he kept pushing back as long as he still had the job. Total office politics. Luckily the file format was in plain text and all I had to do was interpret some odd fields asking around. I was never paid (it was a favor), but it felt so good to know that this other person knew it was me who did it.