Em site da Avira :
Currently, the Avira products are not ready for Windows 8 and Windows Server 2012 (Built on Windows 8).
Avira is working closely with Microsoft to achieve compatibility for the products as soon as possible. Therefore, it can be said with certainty that the Avira products will be compatible with Windows 8 in the first quarter of 2013.
Essa mesma informação deve ser mostrada quando você clica no botão "Verificar se há soluções on-line" depois de não instalar no Windows 8 [ fonte ].