Hoo boy, this is a big one. One of the main points of the book, after all, is that viruses are everywhere. We're talking in human bodies and online, so when we say everywhere, well, we mean it. Viruses in this book are symbolic of loss of control—and conversely, taking control—whether bodily, brainily, or technologically speaking.
Keep in mind that virus can mean a few different things. In the epigraph, Stephenson gives us some definitions of the word from a dictionary:
Venom, such as is emitted by a poisonous animal. 2. Path. a. A morbid principle or poisonous substance produced in the body as the result of some disease, esp. one capable of being introduced into other persons or animals by inoculations or otherwise and of developing the same disease in them….3. fig. A moral or intellectual poison, or poisonous influence.
So from the very beginning of the book, Stephenson keys us into thinking that viruses can be physical things—like diseases or illnesses—but also moral or mental things that can cause you harm.
If we pursue the moral/mental line of thought, we get to the idea that viruses can reside in our brains as pervasive and recurrent ideas that influence our behavior, whether we like it or not. Translating this over to computers—which are equally sights of infection in this book—we can see this as infection of software, which is intellectual property and includes the data on your computer. And since in the technological world, a computer virus can damage your hardware, we return to the idea that a virus has a physical effect, on both computers and human bodies.
It seems that viruses are an essential part of life. As Hiro explains it: "'Any information system of sufficient complexity will inevitably become infected with viruses—viruses generated from within itself'" (56.16). Listen up, Shmoopers, because he doesn't just mean computer systems: Life counts as a complex information system, hence all the diseases that plague our species and many others.
If you've ever clicked on an Internet meme, then you've participated in the spread of a viral idea. Congratulations. In Snow Crash, however, viral ideas pack more of a punch because in the case of the Asherah cult/virus, they can have a biological component up in the mix as well. In other words, we're talking mind and body control.
Interestingly, the Mafia takes a stand against not only Snow Crash, but also viruses in general. As Fisheye explains to Hiro:
"[…] the Mafia way is that we pursue larger goals under the guise of personal relationships […] This is how we avoid the trap of self-perpetuating ideology. Ideology is a virus." (48.20)
Let's unpack that "Ideology is a virus" phrase right quick. Ideology is a system of thoughts/ideas/beliefs (think: Christianity, Marxism, veganism) that becomes self-organizing and self-policing. This has benefits—yay for organization—but also drawbacks, which can include an us versus them mentality. It's easy to demonize or dehumanize people who aren't like you when your belief system tells you that they're the enemy of your lifestyle/religion/social class/whatever, but in doing so, we stop being critically engaged and start running on autopilot.
You know what makes our own engagement impossible and takes over the show once it arrives on the scene, effectively putting our bodies on autopilot? A virus. Seriously—just think of the last time you had the flu. We're pretty sure you puked whenever that virus told you to, no matter how badly you didn't want to. The same can be said for ideology, except instead of making you vomit, it can impact where you work, who you're friends with, how you dress, etc., and once you've committed to it, it's easy to just do whatever an ideology says you should.
So while Fisheye may not have thought of it in quite these same terms, he's basically saying that humans inoculate themselves against ideological viruses by having personal relationships. When the people around you have names and histories that you know and take interest in, you're less likely to see them as interchangeable, or in simplistic terms, like you are good because you do what I do or you are bad because you don't like what I do. Think of personal relationships as like the white blood cells resisting ideology's infiltration.
Viruses are major players in this dystopian novel, and you don't have to be a biologist or tech-wizard to understand that they're pervasive, shaping the experiences of everyone—and pretty much everything—we encounter. While we think we've got a good grip on when a virus attacks our bodies or our computers, however, the book still leaves us haunted by one question: How do you know when a thought is your own? It's a doozy of an issue, and one that can't help but implicate both us as readers, along with our ideas. Yikes.