I've done a bit of digging. I'm fairly compulsive about spyware scanning so as I suspected, it's not on my PC. It's on the sites themselves. For example you can
see it here Notice the double underlines?
A stroll through their HTML code turned up something called
intelliTxt
The web abounds with
comments on intelliTxt.
There is also a note about
how intellitxt is often taken to be Top Text (nice call GD).