“crackme” files—code games that programmers wrote for one another to test their reverse-engineering skills. Coders would write small programs coated in an encrypted shell, and reverse-engineers would have to crack it open and bypass other protections to unearth the secret message hidden inside, then send it back to the author to prove that they had solved it. Viruses and worms were just another type of crackme file in one sense, though some were more sophisticated than others.
