Zombies! What does this make you think of? The living dead prowling around cemeteries at night? The apocalyptic mood of “The Walking Dead”? What all zombies on the TV have in common is that they can only think of one thing – human flesh. Viewers anxiously follow as masses of submissive undead wander across their TV screens, considering themselves safe on their sofas at home – while digital zombies are roaming freely on the Internet and carry out remotely-controlled attacks. We will show you what zombies from films and the television have in common with cyber zombies.
But even though cyber zombies don’t feed on a compulsory brain-based diet, they are still dangerous. A zombie PC is a computer that carries out actions under remote control, without the actual user intending this to happen. This manipulation can be the result of a drive-by download, where the user unwittingly downloads malware. If a backdoor gets onto the computer in this way, criminals can use it to infiltrate the system and remotely control the PC. Because of the uncanny parallels between the undead in Hollywood films who have no will of their own and remotely-controlled computers, security experts call these infected PCs “zombies” as well.
A zombie PC is also called a bot – and a collection of individual bots is a botnet. The network of computers can reach enormous dimensions – sometimes thousands or even millions of zombies are combined into a network. BredoLab, one of the biggest botnets, comprises over 30 million separate devices. This network alone includes ten times as many cyber zombies as people who live in Berlin.
The so-called botmaster is, metaphorically speaking, the puppet master pulling the strings of the PC puppets. He controls individual zombies from his computer and tells them what to do. Some are programmed to send out large volumes of spam. Other bots spy on the users and become “sniffers”. They send the data, credit card details or passwords they have captured to a target specified by the botmaster. The data is offered for sale on the Internet black market – or used directly to plunder victims’ bank accounts. A Brazilian gang managed to extract almost five million dollars from other people’s accounts in this way. But spying on data is just one way a botnet is used. Criminals use zombies for numerous different activities, for example DDoS attacks that deliberately overload servers or computers. Such bot attacks are offered as a service in relevant forums.