I hear this all the time:
Customer: I didn't click on anything, I don't know how that got installed.
Me: Yes, but program A is on your PC.
Customer: Oh, yeah...I installed that! They say proudly, all smiles and such.
Me: Yeah and did you uncheck the boxes that said we are going to install these other programs?
Customer: I don't think there was anything like that.
Yeahhhh....