I don't understand... are you trying to block an "xray hack" ?
If so, download Anti-Xray from bukkit.
no no no ! I am trying to reverse bypass this protection!
On the server with the mod industrialcraft your minecraft.jar not work ...
The server rejects the connection with the inscription bad packet 250, and when a conventional minecraft.jar c mod x-ray the server rejects the connection with the words 'you have banned for the use of x-ray'
If you do not understand again, just put the files for x-ray mod...