NYT 9/4: Heart of Darkness, on a Desktop: "More and more [Windows] PC owners are discovering software lurking on their computers that they had no idea was there - software that can snoop, destroy or simply reproduce itself in droves."
This is pretty much a Wintel problem; though I think there is some spyware for Linux the problem is much smaller. This is not a Mac OS problem.
As usual, buy a Mac.
Overall this is a fairly poor article. There are a number of programs that check for unexpected communication activity, the author should at least have mentioned them. The phenomena is interesting, however, because of inevitable analogy to ecosystems. This software is parasitizing the ecosystem of home computers. A form of natural selection is in action, with mutation arising from human intervention.
It's very, very, hard to avoid such spyware. I almost got caught on a Win2K box when downloading an update to the PalmOS from Palm Inc. If Palm is covertly installing spyware-like software, then Window users are truly doomed.
In our home we're moving to Macs for client and server machines, a non-connected (no network connection, no Internet connection, no floppy drive) Windows 98 machine for children's games and software, and a single WinXP workstation that is sealed to the max and accessed only by our most paranoid user -- me.