Here's the thing -- experience is always the best teacher. Unlike PC owners, Mac users are simply not used to dealing with rampant malware, experts say. As a result, Mac users are much more likely than their Windows counterparts to underprotect their machines, or not protect them at all. PC owners acknowledge, in fact expect, that their machines will be riddled with security flaws, which leaves them susceptible to all kinds of malicious code. If their PCs are a little slow or erratic, most will simply download that antivirus upgrade they had been meaning to install and go about their day. Not so Mac owners, who often assume that they're perfectly safe, even when they're not. So the upshot is, Mac owners don't know what they don't know. And that could likely be the biggest mistake of all.