This is a patently false statement. They will cite examples of animated cursors and other programs that people download and install (that come bundled with spyware) but I was INFECTED (yes, infected with such a spyware VIRUS) when I typed a "soundalike" webpage name for some site.
Some clymer bought a name that would deciptively look like the site I wanted to visit (a Google search took me to the right page). When I got to the false page I saw what looked like a squater's search engine. I never "approved" the installation of any software.
The company knew that they had installed something you and I did not want because these programs will reassert themselves if they are not entirely removed (hidden files deleted). In your case there were even alterations to your system settings so that you could not easily make the change.
Your computer was hijacked and raped by some scumware company.
Don't try to sue though because the advertising lobbyists long ago got the legislation that they wanted from elected officials.
We know it is malicious software of the same nature as a "virus" but the tech-ignorant legislators believe otherwise. Only now (that it is too late) are any laws being drafted to stem the practice (which will just go offshore and out of "our" reach).