Live Technician Pop-up appearing to be from Microsoft Internet

An unwanted pop-up which appeared to be from Microsoft alerted me that my entire computer network was in imminent danger of crashing.  I called the emercency number listed and was told that they were the official representative for Microsoft and that Microsoft did not have a support system.

I was told that there were two Trojan Horses taking over my computer and that it had to be dealt with immediately.  After a lot of haggling and converstions with both the "certified technician" and the "supervisor" (both with mid-Eastern accents) I agreed that I would pay the $179.99 to rid my computer of the virus.

I explained that I had the Norton protection plan and was told that Norton software would not remove the type issue I had. It was late at night and I was frightened and tired,  but I watched the whole 2 hour "clean-up" process as they scanned my computer.

They basically used several types of free software to scan and remove a few cookies, etc..  The next morning after realizing that I might have been scammed, I ran the Norton program and everything was clean and normal, so it looks like Live Technician did what they said they would do.  The problem is that I did not need the service. Their scare tactics and downright misrepresentations quality this company as real scam artists.

How can a pop-up prevent you from accessing all other programs on your computer.  Once the pop-up appeared, there was nothing I could do to get off the screen.