Would your antivirus software happen to be Avast? We hear it is quite buggy and finds “viruses” where there are none.
I’m not sure how to advice you. You can of course safely install Animation Paper. However, in this situation, in order to do so you will have to turn off Avast, which is not recommended of course.
I personally don’t know Avast, but maybe there’s a setting to let Animation Paper install without disabling the virus protection in general?