well my frined, what you have stated is that u have the Keygen as a virus, that is usual in all keygens, and, if u dowload avast from the official page, it wont have a virus. I assume u have donwloaded it from a warez site or some illegal site, because of the name of the file u mentioned.
I have to state, that the official avast exe is free of malicios software, spyware, adware, and all kind of bad stuff, so please, download avast from here:
http://www.avast.com/esp/download-avast-professional.html and also, dont use cracked or keygened software, because most of the time it has bad stuff inside the executable file.
Plz, support avast by buying a legal key, but besides that, the thing is that the file u are using is a keygen, and almost all keygens are marked as virus or something like that. So, take care. See ya!