if I browse to web.de or gmx.de there is a message on the top of the page
"Die Sicherheit ihres Rechners wird durch ein Chrome Add-on eingeschränkt. Sicherheit wieder herstellen"
The button sends me to http://www.browsersicherheit.info/ This website was created by 1&1 Mail & Media GmbH , the headquarter of gmx.de and web.de.
The user should uninstal "dangerous" Add-ons like Adblock Plus. Because these Add-ons are verry, verry bad..
The message I talk about looks like a browser-message of Chrome or Firefox. But it is created on web.de or gmx.de via Javascript, maybe someone can make a script to block it^^

Thank you.