Floatover ads/HOSTS URL blocking

I am running Win XP Pro SP1 and at the moment I'm using Avant browser 10.0 build 168.

On some webpages I visit keywords are underlined in green and moving the mouse over them as I navigate causes floating text boxes to popup. The information in the floatover boxes is all advertising.

The floatover boxes have the caption "What's This" in the upper right corner. Using the cursor to floatover that caption, the URL in the lower left corner of my browser window displays:

http://www.vibrantmedia.com/whatisIntelliTXT.asp?ipid=1368&cc=us&server=us.intellitxt.com

I had the same result using the Maxthon browser last night. I went to modify my HOSTS file. WWW.vibrantmedia.com was already in my HOSTS file, but us.intellitxt.com wasn't. Adding intellitxt.com to my HOSTS file and relaunching my browser, the keyword underlines and floatover ads diappeared.

Switching today to Avant because I wanted to allow fewer restrictions on javascripts without having to change security settings, the keywords/floatover ads are back. I doublechecked my HOSTS file and the vibrantmedia and intellitxt domains are recorded there just as they should be.

So I don't understand what the problem is now. A webpage which has many examples of this advertising is http://forums.superiorpics.com .

Thanks in advance for your help.