There are many plugins that stop it, but most don't really work too well. It's much easier to just watch them. Speaking of, OpenInv and SimplyVanish (since VanishNoPacket causes lightning whereas SV does not, much more secretive) are very good for catching people.
iConomy 7 isn't real, it's iConomy6, and I have the .jar that works with 1.3 on my desktop XD
I can create a special channel for all of these talks