All this spyware, viruses, and trojon are design to effect PC only. There isn't any virus for Mac, sadly the truth behind it even mac fans refused to belive is that not enough percentage user using Mac, so no one create virus for Mac.
Try using LimeWire, or Kazaa the king of Windows detroyer and you will Garantee to force reformatting your hard drive and re-install OS within severals days.
There are ZERO effective self replicating viruses capable of affecting Mac OS X, but there have been recent proof of concept developments in a small handful of trojans that could in fact affect your OS X system.
Fortunately, as long as you only install software from known reliable sources, the risk in minimal.
Downloading pirated software from P2P networks does put you at risk because anyone with the skillz could re-label a destructive program as a popular application, just waiting for you to type in your administrative password.