This is what Microsoft describes Smartscreen filter as;
I don't want to sound sarcastic or anything like that, but if your browser is telling you that something you are attempting to download is likely to be malicious, would you not consider that warning and decide that the pc_check_tuning_2012_81mb_us.exe file is somewhat suspect, and so halt your attempts to download it?
I know I would.
You say you purchased this for $4.95. CNET does not sell software. CNET lists software titles at Download.com for users to download if they wish, for free. There will be cases where software is "free to try" and in which case the software developer will require you to purchase the software from them if you want to keep using it. But that is between you and the software developer.
So, I do not understand how you could have paid for this software before downloading it.
Are you sure this was software listed at Download.com, or was it some advert you clicked on which took you to some other web site?
I get a message that pc_check_tuning_2012_81mb_us.exe could harm your computer. I went to Tools and added download.com to my trusted list, but continue to get the same message and cannot download the program I purchased for $4.95.
I have Windows 7 and use Internet Explorer.