Malware distributors do that every day; it's nowhere near as complicated as you might think.
With all the belt&suspenders, doublechecking, skeptical folks we have here, I'm really a bit surprised that anyone would go for one of these "discount" software operators on something as important as tax software, especially since you will be giving it so much personal and financial information and you won't know what else it might be doing on your computer.
Obviously, we all want to save a buck when we can, but that's not where I would want to do it. There will be enough legitimate discounts available in the next couple of months that I think it's worth waiting for them.