You have probably heard it said that there are more viruses on windows, particularly if talking to somebody using a mac.

That is correct.

Hold on now, put that pitchfork back in your pocket. How did you fit a pitchfork into your pocket, anyway?

There are far more viruses that target windows than mac, or any other operating system for that matter. The typical explanation given for this is that macs are more secure than windows, either because windows is insecure, macs are very secure, or both.

In the past, that was true. Windows had lots of security problems. In many ways windows had a culture of insecurity, where security wasn’t a concern in software design at all. For example, until Vista the admin user ran every program as admin whether it needed those permissions or not. This has since been rectified with UAC (User Account Control), the “are you sure” box that darkens your screen. The trend continues with internet explorer, which has also had countless security problems. Windows also autoran programs on optical disks by default. This is by no means a comprehensive list, either.

So windows had security problems. Fortunately, Microsoft did eventually learn that security is important and has since fixed these many problems.

As it stands today, the desktop operating systems are roughly as secure as each other, at least in terms of operating system security. Typically when you get a virus these days it is either caused by user action (i.e. your fault) or it is caused by a program you use (such as your browser) and not the operating system itself.

Despite this, windows still gets the lion’s share of viruses. Why is that?

By and large, the answer is economics.

The purpose of most viruses is to make their creators money. Finding security flaws and exploiting them takes time, and time is money. Virus creators are looking to get the most bang for their buck. They want to minimize the amount of time it takes to create the virus and maximize the number of computers they infect. With these goals in mind, what would be the best operating system to target?

Windows. It is always windows. Always has been, and presumably will be in the future as well. This is due to the market share.

At the time of writing, windows has roughly 90% market share. In fact, windows has had this large market share for well over a decade. If you pick a random computer, 9 out of 10 times it will be running windows. And, 9 out of 10 times, your virus will be able to infect it.

Furthermore, windows has typically maintained better backwards compatibility relative to mac and linux. If you take a ten-year-old program, odds are pretty good it will run on modern windows more or less the same. Not so with macs, and linux has so many distributions even getting present-day software to run can be a challenge.

So most people run windows, and it is easier to make programs that run on the windows ecosystem. Thus, virus creators have incentive to target windows more than other operating systems, and they do. This is the primary reason for the disparity. The effect of this targeting can be seen.

Let’s say you go to a file-sharing website to download a file. You are using a mac, because Ronald McDonald told you to in a dream. Seems legit. So there you are, downloading your file. Which of the five download buttons is real? Oops, you clicked the wrong one. But the virus didn’t run, because it was made for windows and you aren’t using windows.

Situations like the above example are fairly frequent. Things are just made for windows, because they are the most likely to succeed. You know, like me.

That’s not to say that viruses only exist on windows – viruses exist for all operating systems. They just exist in far greater numbers on windows than anywhere else. That could change, though.

Let’s imagine that macs do gain market share, up to 30%. At that point, while they still wouldn’t have the greatest market share, it would still be large enough to be worth targeting. mac viruses wouldn’t be unheard of anymore.

In effect, macs are secure because so few people use them.

Market share isn’t the only reason windows is targeted, though – just the biggest.

For example, let’s compare windows and linux. Imagine that, for whatever reason, every virus creator decided to target linux. I predict it wouldn’t be as bad as windows, for a few reasons.

First, linux had a different design philosophy than windows. Linux was a clone of unix, a time-sharing operating system. Back then, computers were large and users interacted with them by using terminals. Multiple users could be logged into the system at the same time.

When there are multiple users on the same system, there are a number of security concerns. For example, what if one user alters the files of another user? What if a user changes important system files, preventing use of the system by anybody? Unix had to be secure from the start to address these challenges. Windows, on the other hand, was originally a single-user system and only became multi-user later. It didn’t originally have file permissions at all. While windows has since fixed these problems, it doesn’t have quite the same security culture as linux.

Additionally, most computers are shipped already running windows. In order to be running linux, you typically have to install it yourself. This presumably indicates at least a somewhat tech-savvy user who is presumably less susceptible to viruses.

Finally, the manner of installing software differs. On windows, you typically have to search for particular software and navigate to a website to install it. This introduces the possibility of downloading it from a less-than-legitimate source, and it may be infected. Linux, on the other hand, has gained many of its features from its use on servers, including a package manager. The package manager is similar to contemporary app stores. The programs in the package manager are reviewed and known to be secure. This allows secure installation of new software.

These aren’t the only potential differences, but serve as an example of how market share might not be the only factor.

While market share isn’t the only factor, it is still the largest by far and serves as the primary explanation for the virus share among desktop operating systems.