A German ISP tampered with their DNS - specifically to sabotage my website

A German developer created a website to expose blocked domains by the CUII (Copyright Clearinghouse for the Internet), a private organization that decides what websites German ISPs should block. After publishing an article about CUII's mistakes, Telefonica (o2's parent company) modified their DNS blocking mechanism, making it harder to detect blocked domains. The timing suggests this was done specifically to sabotage the transparency tool, as Telefonica first tested their own domain on the website, then changed their blocking method two hours later.