MAC Addresses are piss easy to spoof. I suggest you leave Jagex to do what to do instead of trying to recommend Jagex to use flawed methods. They after all know what they are doing. And not only that, but what if its a shared or public computer? If its a public computer, they wouldn't use the same one over and over and over. Also, I don't think its feasible to leave a macro running on a public computer for hours? Anyhow, MAC Adresses are unique. IPs are not necessarily (until IPv6, then they'll be able to be unique). The idea was just to know which accounts are linked together. Just checked, Java doesn't have a native method to get MAC addresses until version 6, so Jagex wouldn't do it anyway. But nabbing the idiots that create a new account solely to macro would give me some satisfaction. MAC Addresses are unique, however they are not hard to change (depending on Ethernet card) or to spoof it. Its no more guaranteed than tracking by IP. Hardware serials would be the best way to go (even then you can still spoof these), although I doubt that's possible with native Java specially without the signed client.