Rustock Botnet was a big computer network full of computers that were used to do bad things on the internet. Each computer in the network was used to do the same bad things, like sending spam emails and infecting other computers with viruses. All these computers were secretly controlled by a few people, and they used Rustock Botnet to do their bad activities. Rustock Botnet made it easier for these people to do bad things on the internet, because it allowed them to control many computers at the same time. Unfortunately, Rustock Botnet made it harder for people to browse the internet safely, because the computers in the network were constantly sending out spam emails, trying to infect other computers, and generally making the internet a much less secure place. Rustock Botnet was eventually shut down by security experts, which is a good thing for all of us who use the internet!