I am interested in the legalities of this. There are other areas where legality of a sale is dependent upon the seller's knowledge or beliefs about the buyer's intent. For example, drug paraphernalia… if you sell someone a pipe in Mississippi, and they don't say anything or they mention tobacco, that is fine. However if they said they wanted to use it to smoke cannabis, completing the sale would be distribution of drug paraphernalia, even though it's the same item.

Yes, this is probably a better example..

The article says he was selling his software by advertising it as a tool to steal credit card and banking information from people infected by it. There is no legitimate purpose for that.

This is like a gun manufacturer advertising their gun as "Great for robbing liquor stores!"

Guns have plenty of legitimate uses. Self defense, hunting, and recreation. Guns aren't intended or even primarily purchased and used for criminal purposes. They will probably try to argue this tool was.