Many people that switch or stick with Apple often have the notion that a Mac is going to be more secure than a standard Windows machine. While for the most part this is true, Macs are still vulnerable to attack, and this was recently demonstrated at a black hat conference in Las Vegas. The attack occurred over a wireless connection, and abused the default behavior of Macs (and often PCs) to automatically scan for access points in the area:
While the exploit is equally dangerous to PCs, the use of an Apple machine drew the attention of the blogosphere. Apple systems are traditionally seen as safer than PCs from threats of hackers and viruses--a notion that Apple has touted in ads for its systems.
The people who demonstrated the attack aren't giving full details and aren't showing how to reproduce it, which is probably for the better.