I wouldn't say that Apple ever had really good security on their products. In the past, the main deterrent for would-be hackers was that fact that the Apple install base was so small. IMB and Microsoft were essentially in 90% of the computer market and there was no point in making a virus for such a small share compared to other PC's.

Now, mobile devices with Android and Apple are a big target. And since Apple has seen gains in the desktop environment, they have more people willing to find exploits in their systems.