While Apple's install base is steadily growing, I still think they have a significant advantage in obscurity that grants them security.
i.e. Why do virus-writers target Windows? Sure, it has the largest install base, but Windows also runs a lot of servers and embedded systems. These two things are the real jackpots. What's taking control of one person's computer compared to taking control of a server with credit card information or a system running a billboard in Times square? Apple doesn't do embedded systems and their servers, while some do exist, are exceedingly rare.
Is security through obscurity enough though? That depends on who you are and how interesting your data is.
What do you mean by obscurity? Which level of the system are referring to? You seem to indicate that Windows is somehow open. Can you explain what you have in mind?
I said what I meant by "obscurity" and I did not say anything about Windows being open, but I'll restate things in other words in case it clears things up.
OSX and iOS are used predominantly to run personal computing devices. In addition to PC's, Windows also runs a significant number of the world's servers (although Linux dominates here) and embedded systems (see http://www.microsoft.com/windowsembedded/en-us/windows-embed...). Despite OSX and iOS gaining significant market share, virus-writers may still find that the sweetest targets are disproportionately running windows. OSX and iOS are more "obscure" in the sense that they don't run many of the systems virus-writers want to target.
i.e. Why do virus-writers target Windows? Sure, it has the largest install base, but Windows also runs a lot of servers and embedded systems. These two things are the real jackpots. What's taking control of one person's computer compared to taking control of a server with credit card information or a system running a billboard in Times square? Apple doesn't do embedded systems and their servers, while some do exist, are exceedingly rare.
Is security through obscurity enough though? That depends on who you are and how interesting your data is.