The instaler u are trying to use is corrupted or incomplete.
This could be result of a damaged disk, a failed download or a virus

you may want to contact the author of this installer to obtain a new copy

It may be possible to skip this check using the /ncrc command line switch
(NOT RECOMMENDED)

1.
Nein, ich habe kein viruse und der download wurde normal beendet

und

2. wie macht man dieses /ncrc command line switch?