Heart of Darkness, on a Desktop

Heart of Darkness, on a Desktop: "The alien programs extend well beyond viruses and worms - so named because of the way they spread, as the most familiar carriers of malicious code - to new categories known as spyware and adware. Indeed, the number of home PC's that are infested with alien software that comes in over the Internet and installs itself without the knowledge or consent of the PC user is increasing at an alarming rate.
Richard M. Smith, a computer security expert in Brookline, Mass., estimates that one in every two Windows computers has unsolicited software lurking within."

Don't run KaZaA; do run Ad-Aware