It is not only the computers of the future that pose a threat to security, it is also the legacy of the past. Over the past two or three decades, it has become clear time and again that the majority of Internet users are struggling to replace insecure protection mechanisms. It usually takes more than ten years to introduce an improved security protocol on a large scale. If the fear of quantum computers helps to overcome this inertia, i.e. if the efforts of post-quantum cryptography are conducive to “crypto-agility”, then these novel computers have proven to be useful – even if they will never exist.