Plague carriers: Most users unaware of PC infections -ZdNet
A study of home PCs released Monday found that about 80 percent had been infected with spyware almost entirely unbeknownst to their users. Spyware can allow unknown intruders steal important personal or financial information from victims' computers, and some allow the attacker to have full control of the systems. When networked together, the systems can form a digital army, known as a bot net, that can be used to attack other networks.