From everyone.net's login page:
What the hell is an "Interstitial Advertisement"???????
New Interstitial Advertisements
Starting on February 16, 2001, we will be incorporating behind-the-browser interstitial advertisements in the Plug-in-Email service and Control Center pages. These interstitials will appear once per login, and will not affect the email or Control Center service.
What the hell is an "Interstitial Advertisement"???????