I hardly think that Avast may corrupt the files, it's just that it adds time to the installer time if Avast begins a search for that specific file during the installation.

Either put an exception in Avast's File System field or turn it off temporary during download and installation.

Oh thank god, I don't have to spend another several hours re-downloading everything again. Now if I can just get my replacement power supply in the mail and not fry it with another one of my mistakes of halfway plugging the power cord into the back of the PSU and not realizing the cord was loose.