Contrary to popular belief, Apple operating systems are at least as vulnerable to attacks, hacks and cracks as any Windows system. The perceived invulnerability is based on the paucity of attacks on these systems, as they have been less popular, specifically in the realms of government and business. But as Apple products have grown in popularity, they're increasingly attractive targets to the bad guys.
Unfortunately, another drawback of Apple products is that they require pricey software; however, Sopphos has now made its excellent Mac Anti-Virus product free for download and use by Mac home users.
For more free software choices, consult the Freeware page at Stuff Economics.