Spyware does not directly spread in the manner of a computer virus or worm: generally, an infected system does not attempt to transmit the infection to other computers. Instead, spyware gets on a system through deception of the user or through exploitation of software vulnerabilities.
A common trick is to covertly install the software during the installation of other software you want such as a music or video file sharing program. Whenever you install something on your computer, make sure you carefully read all disclosures, including the license agreement and privacy statement. Sometimes the inclusion of unwanted software in a given software installation is documented, but it might appear at the end of a license agreement or privacy statement.
Most computer users are tricked by Spyware, when you decide to download something from the internet. You install some desirable software that you think you really want and could use, but all along it could be piggybacked by undesirable software.
Mario Armstrong is a technology talk show host, writer, consultant and public speaker that explores how technology impacts the way we work, live and play. He is heard on NPR, XM radio and seen on WMAR-ABC2 TV. More online at: www.MarioArmstrong.com. 
