There are more than one blacklist out there, and they feed off of each other. So getting listed on one means that - over the next day or so - you will get listed on 20 of them. Getting de-listed involves generally going through the dispute process on every individual blacklist. Anyway, it isn't your machine. It's your ISP that has been compromised. There was probably a PC that got infected in your IP range and was spamming as a part of a botnet while the owner of the PC was at work, or whatever, and so every IP in that mask was blocked at the ISP level. Still, the power is in your ISP's hands. An individual protesting an RBL listing is mostly going to be ineffective, because they block whole subnets, not usually individual IP addresses. Check with your ISP and ask them whats up.