[color:"orange"]I believe there is a law structure around this, I'm unsure of the specifics, though.[/color]
Unless the copyright holder specifically grants permission for someone to modify or re-distribute something, then anyone who does so is in violation of the law (in just about every country). The only thing a piece of software being abandoned does for pirating is to make it much less likely the copyright holder would take any action against them. That said, it is easier to justify re-distributing abandoned software.
FYI;
10 Big Myths about copyright explained 
