Something Norton Missed-Took over my PC-Personnal Security software downloaded

Hello,

New to boards. I just was browsing online and all of a sudden. I receive a pop up window that my Windows Security Center has installed "Windows Personal Security". It placed an icon on my toolbar and desktop. Then it prompted me to pay 89.95 for protection. I denied. This rendered my pc unusable. I could not get desktop icons to show up, I could not get online (everytime I opened internet explorer, it blocked the site I was going to and prompted me again to pay up) This icon was a blue shield with line diagonally across it. I find it hard to believe that this was a legamite Microsoft Windows security download. I did a complete computer scan with Norton and it did not detect anything wrong! All my definitions are up to date. I finally rebooted in safe mode and did a system restore back a couple of days ago. This seemed to solve the problem.

But my major question is, why did Norton allow this software to download to my pc? Why didn't it detect this?

Anyone else run in to this?

Thank You,