Malware, or malicious software — and how to prevent it from harming your Mac — was the topic of this chapter. I began by describing viruses, worms, Trojan horses, and several other common kinds of malware. I explained how your Mac can transmit malware to other computers without becoming infected itself and showed how to determine your level of risk for infection or transmission. Because most malware damage results from poor user decisions, I showed you how to use common sense to avoid the vast majority of malware. For times when common sense isn't good enough, though, I also described several popular Mac applications for stopping malware in its many forms. I introduced you to outbound firewalls — programs that watch for potentially illicit network connections — and explained some things no anti-malware software can do for you. For Mac users running Windows using Boot Camp or virtualization software, I finished the chapter with a discussion of extra steps needed to keep your computer malware-free.