The word “botnet” is being ever more frequently mentioned in the same breath as terms such as hacker, malicious program, malware and cyber-attacks. At first glance, the definition sounds harmless: A botnet is a combination of many different devices that are connected to the Internet. As so often, the devil is in the detail, because the computers in a botnet run automatically and are controlled from a central location with the aim of spreading malicious programs known as bots. The illegally hijacked computers are therefore often referred to as zombie PCs, because they are controlled not by the actual owner, but instead by hackers.