The only PUP no one loves
They're called PUPs—Potentially Unwanted Programs—and they sneak onto your system as accessories to the program you actually intend to install. They're annoying, and they can result in slower performance, space-stealing browser toolbars, annoying pop-ups, and even loss of privacy.
You don’t have to give up free software to avoid PUPs, but you do have to pay attention. Each PUP first appears as a trap in the desired program’s installation wizard.
Ian Paul recently recommended a program called Unchecky that attempts to uncheck installation options for you, but I prefer just being careful. Here are some tricks and traps to look out for during software installations.