I have to say that I don't understand this point. I used DOS quite a bit (My first computer was a 386SX 33, ages ago), and AFAIR DOS virii needed no source code to infect executable.
Back in those days, the criminal element who wanted to infect .exe files wasn't as prevalent as it is today.
Look, whatever argument you're trying to make, it isn't going to work. I'm not going to release my source.
And if you're unqualified to write the program, why did you want my source code in the first place?
End of discussion.