Posters who slag Windows off as 'insecure' and claim OS X has a lack of malware due to it being UNIX based have literally no idea what they are on about. They throw around the word UNIX like it explains everything when in reality, malware and viruses have been made for UNIX based systems longer than they have for Windows. In fact, there are very few true viruses around for Windows nowadays, the vast majority of them Trojans relying on users freely installing them through lack of knowledge, just like OS X.
In reality, it is marketshare that dictates how many malware attacks you expect to receive. Anybody who makes malware for a system that nobody uses is a complete moron. Especially when it is ad based.
Regrettably you're the one who comes across as having literally no idea what you're on about.
There are many, many, many real viruses for Windows. Cryptolocker is possibly the worst I've encountered. Not only that but there are hidden payloads in .scr files (screensaver), .doc, Excel attachments -- the lot. These are all emailed as attachments and none of them are detected as malicious items, even through VirusTotal. But run it and you're scuppered. There are payloads which automatically download and run Trojans in addition to a number of other nasties, just by exploiting Javascript, Flash, or through Internet Explorer.
If I may offer a gentle reminder that Internet Explorer is the default browser on Windows. Many people use it, and it's patched weekly to sort out the slew of security holes in it. The fact that you could just browse an infected website and unwittingly get a payload downloaded/installed in the background isn't a virus to you? It's a very real, and very common, issue.
The additional truth of the matter is that Windows, under-the-hood, has practically remained unchanged for 2 decades. The registry layout in Windows 8.1 is almost identical to how it was in Windows 95. It's very, very easy to attack the registry and edit changes. I mean changes in terms of adding a payload to when explorer.exe runs, simply by hitching on an executable file or run a download with the shell hidden, so it's all going on in the background with 0 knowledge or permission from the user. A lot of the nasty Metropolitan Police viruses (not malware, viruses) do this. It also means that if you're logging in through Safe Mode it'll automatically shut down the computer. That's through HKLM or HKCU\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon, for your future reference.
Jesus, I don't even want to get started on services being deleted in the registry, firewall entries being deleted, Internet Explorer being bricked, and the ZeroAccess changes that are soooo frustrating to fix.
Microsoft have an obligation to supply an incomprehensible amount of backwards compatibility due to how long they've been in the business and how many people rely on their software. This alone opens up a wealth of security problems.
I can go on, and on, and on, and give you multiple examples how Windows security issues are not just from people downloading malware. However I feel I may just be wasting my time, thanks to your general (and I'm assuming unfounded) assumption that it's a marketshare/malware issue.