Sigh..you kids don't understand packet editing at all do you?
1. What is a packet?
Packets are bits of information sent and received by the client and the server as a means of communication with each other. For example: Say I have a very simple client/server relationship, my client consists of a program with a single button. When the user of my program presses this button, I want to know and record it. So I make the client send a packet to the server once the button is pressed, and once the server receives this packet, it proceeds to record that the user has pressed the button.
2. What is packet editing?
Packet editing is simply manipulating which packets are sent to the server/which packets to receive. This can be very useful. For example, the server probably sends my client a packet when another player shoots me. With a packet editor, I can choose to block this packet. Meaning when this packet is sent to me, my packet editor filters it out and my client act as if I haven't received this packet. Effectively giving me god mode. (this can obviously be patched serverside, though)
Packet editing does not TOUCH Nexon's server nor violate their intellectual property in any way. I am not modifying or distributing Nexon's property without permission in any way. Now TECHNICALLY .rez editing is 100% illegal since you are in fact modifying Nexon's intellectual property without their permission and most likely, redistributing them. Hacks are also 100% legal since the only thing it violates is the Terms of Service, which is not a legal nor binding contract (Unless of course you hack by editing Nexon's original files, Engine.exe or any of the rez files). The only thing they can do to you for disobeying is denial of service. AKA a ban.
Trust me I would know this stuff, I used to be admin of DestinyMS (MapleStory private server) and we've dealt with many legal issues with Nexon which we have survived. We've pretty much ignored all 2 or 3 (don't remember) C&D's they sent us. And if you call BS on me just register on DMS forums and PM iamSTEVE, it's me.