If you come across such things, I strongly recommend that you not download/run these kinds of programs.
Well, even if it's clean, I can tell you that editing packets won't do you much good, because every action your client sends to the server, gets checked by the server. On another forum I overheard something about how nice it would be if he could keep sending "equip packets" to the server (trying to equip like a hundred different items) but unless if the server is coded very poorly, that kind of meddling wouldn't succeed.
BTW here's a packet sniffer/editor that i believe could be 100% clean, it's from microsoft and I'd say it's legal to use:
http://www.microsoft.com/downloads/deta ... laylang=en
Of course, if you do find any exploits on our shard, abusing them can get you in serious trouble, like on any other game or system. But informing us of things you might find keeps the shard fun even for those who play as the game was designed to be played, and also qualifies for a reward

+Colibri, Administrator of UO Excelsior Shard
Don't know what the purpose of your life is? Well then make something up!

(Old Colibrian proverb)