Ok, they’re not spam but they are just as annoying, and they seem to be growing. They’re offered to webmasters and are commonly called IntelliTxt ads. The company offering them is Vibrant Media. Now, there’s nothing wrong with the company and everything they do seems above-board. They don’t install software on you PC. They also allow a way for users to turn off the ads, although this feature has to be implemented by the webmaster and my experience is that not many do. Other vendors are jumping on this bandwagon too.
There’s and alternative if you use Firefox. You can install the GreaseMonkey add-on for Firefox then install a GreaseMonkey script to block the ads.
Install the GreaseMonkey add-on from it’s page Firefox Add-on directory. You’ll need to restart Firefox before the plugin becomes active.
Then install the “Disable Text Ads” from userscripts.org. These popup ads should now be disabled. Be sure to check for script updates as these ad vendors change their methods constantly and new vendors pop up.