Answer:
A Jtag works this way...
You turn it on
You send programmed files from your PC to your xbox with the codes
You log into Xbox Live
From the moment you log into xbox live you have 4 - 5 hours before you get banned automatically
After the 4 - 5 hours, you get disconnected and banned from xbox live
You buy another kv serial number
You program your xbox with the new number
Rinse and Repeat =D