Yes, Mac notebooks can be hacked, and here's a discussion, starting with a Washington Post article.
However, this is a hack of hardware, not of an operating system, and the same vulnerability exists with all PC-capable operating systems. In addition to having hackable hardware,
1) you have to tell the Mac you will accept any connection from any wireless network,
2) the hacker has to be within the range of your wireless network card, and
3) you have to be running as the administrator of your Mac and not just a user.
Whatever you use, OS X, Windows or Linux, make sure to update your operating system frequently to cover security holes.