Still, security experts aren't so hot on Snow Leopard, criticizing the operating system's default firewall setting of "off", its lack of fully automatic updates, and weak anti-phishing efforts for Safari.  They also weren't impressed that Apple shipped with a vulnerable version of Flash, which downgrade users from the safer current version.

Now one prominent Mac hacker has pointed out a significant difference that makes Snow Leopard less secure than the upcoming Microsoft OS, Windows 7. 

Charlie Miller, of Baltimore-based Independent Security Evaluators, the co-author of The Mac Hacker's Handbook, and winner of two consecutive "Pwn2own" hacker contests is about as experienced as OS X hackers come.  He recently criticized Snow Leopard, stating, "Apple didn't change anything.  It's the exact same ASLR as in Leopard, which means it's not very good."

ASLR is address space layout randomization, a security technology that randomly assigns data to memory to make it tougher for attackers to determine the location of critical operating system functions.  According to Mr. Miller, unlike Windows 7, which features robust ASLR, Snow Leopard's ASLR is half-baked. It does not properly randomize the heap, the stack and the dynamic linker, the part of Snow Leopard that links multiple shared libraries for an executable.  This means that it's much easier for hackers to attack Snow Leopard via memory injection than Windows 7.

Still Mr. Miller offered some praise for Apple.  They rewrote QuickTime X, their video player, largely from scratch fixing many holes and insecurities in the process -- including an exploit Mr. Miller had been saving.  He states, "Apple rewrote a bunch of QuickTime, which was really smart, since it's been the source of lots of bugs in the past.  They've shaken out hundreds of bugs in QuickTime over the years, but it was still really smart of them to rewrite it.  [Still] I'd reduce the number of file formats from 200 or so to 50, and reduce the attack surface. I don't think anyone would miss them."

He also praises Apple's relatively effective implementation of DEP (data execution prevention), another memory protection scheme that Windows 7 also has.  DEP is also present in Windows XP Service Pack 2 (SP2) and Windows Vista.  Still without ASLR, DEP is only so good he says.  He states, "Snow Leopard's more secure than Leopard, but it's not as secure as Vista or Windows 7.  When Apple has both [in place], that's when I'll stop complaining about Apple's security."

So why aren't Macs being exploited left and right and why can Apple still air commercials claiming superior security?  Mr. Miller states, "It's harder to write exploits for Windows than the Mac, but all you see are Windows exploits. That's because if [the hacker] can hit 90% of the machines out there, that's all he's gonna do. It's not worth him nearly doubling his work just to get that last 10%."