Contemporary ransomware Bitcrypt held victims' personal files hostage by encrypting them and charging a fee to reverse this. Bitcrypt's cryptographic design also appeared sound at first glance, using PBKDF2 and HMAC-SHA1 to generate random keys for each file, encrypting them with AES-192, then using RSA to encrypt those keys. Except when the author mixes up decimal and binary, "1024 bits" turns out to actually be 426 bits, and failure ensues. It's always the simple things.