1. A virus writer sends out viruses, infecting ordinary users' PCs. 2. Infected PCs log into an IRC server or other communications medium, without their owners knowing, forming a network of infected systems known as a botnet. 3. A spammer purchases access to this botnet from virus writer or a dealer. 4. The spammer sends instructions to the botnet, instructing the infected PCs to send out spam. 5. The infected PCs send the spam messages to internet users' mail servers.
This is a diagram of the process by which spammers create and use zombie (virus-infected) computers to send spam. The diagram is for use when educating classes about the importance of keeping computers virus-free. It can also be used to explain to learners why it is that so much spam is received in their mailboxes and why unidentified attachments should not be opened. Click on the image for a full size version which you can freely re-use and modify. Print it and use it for your lessons, integrate it into your pages on Wikiversity, or use it in other learning resources and websites. Use the links below to find more images like this one.