The version that was earlier this year, I'm going to guess snow leopard since lion is recent. However it was a flaw in Safari, not OSX, and while that specific hack probably has been patched by now, it is still the first browser to be taken down for at least the last 2-3 years.
I'm really not making a pc/mac debate here, I actually think Macs are very good machines for certain people or in certain situations. However, it doesn't matter what OS you're using, you need to use a secure browser, and Safari ain't it. Use Chrome for Mac, it's updated far more often and is far more secure. You don't have to take it from me, though, you can do your own research and find out what the Mac experts use.