The company in question was writing software which modified executable files to provide, in their words, "various kinds of security". I was never entirely sure what that meant; could have been anything from obfuscation to self-decrypt-at-runtime. They licensed the disassembler in the NASM suite from me to use in their product. I got nearly £2000 for it, which I thought was pretty good going given that it had taken me two days to write :-)

(Well, not exactly. The disassembler was mostly a front end on the enormous instruction table I'd already spent a lot more than two days on; that was where the real value lay, if anywhere. But the two days I spent writing a disassembler front end to the table, simply because it seemed easy and it might come in handy one day, turned out to be well spent indeed!)