My email-provider's website (http://www.gmx.de) recently started linking to the (German) site http://www.browsersicherheit.info/ which basically claims that due to its capabilities to modify a site's appearance, Adblock Plus (and others) might actually be abused for phising. Here's a quote from that site plus its translation:


  Solche Add-ons haben Zugriff auf alle Ihre Eingaben im Browser und können diese auch an Dritte weitergeben – auch Ihr Bank-Passwort. Dies kann auf allen Web-Seiten passieren. Sicherheitsmechanismen wie SSL können das nicht verhindern.


translated:


  Such addons can access all your browser's input and can also forward them to third parties - even your banking password. This can happen on all websites. Security mechanisms such as SSL cannot avoid that.


Ok, they mention other (pretty obviously crapware) addons, but is Adblock Plus really a security threat or do that site's operators simply use the opportunity to try and scare inexperienced users into viewing their ads again?

It is not. This is a FUD (fear, uncertainty, and doubt) campaign by GMX because they want to display their ads. There is absolutely no security risk from the mentioned ad blockers. They added some crapware to the list to make it look more legitimate.

Of course such campaigns are very unusual, especially from such a big and well known company like GMX. Unfortunately, I have no English source at hand (because it's a German only campaign) but since you speak German you may want to read this article at heise.de.

Update #1: United Internet, the company behind GMX, received a lot of criticism for misleading customers by falsely claiming that there is a security risk on their PC. The Wall Street Journal (German edition) named the warnings displayed on GMX and the site they link to a "scare campaign".

Update #2: GMX now says that they will no longer display the link when you use ad blockers but will still display it if you use crapware that injects adverts, the list at the site http://www.browsersicherheit.info/ has been updated accordingly and now lists only a small collection of crapware. This list is by no means complete so it is not a reliable source when you want to know if your browser has crapware installed. However, United Internet still maintains it's position that they do not want users who visit their sites to use ad blockers and said they will develop other anti-blocking methods in the future (German source).
