According to the FAQ the follwing step is required to exchange the ECU

NEW
3. Take that 14-digit Immobilizer ID number (along with your VIN number) to your dealer and request your seven-digit SKC, along with the workshop code and importer number (all this information can be found in the upper-right corner of the Administration screen of the dealer's VAS 5051).

USED
4. Bring both 14-digit ID numbers to your dealer and request both your seven-digit SKC's Keep track of the SKC for ECU#1 and the SKC for the ECU#2, as well as the Date on which each SKC was GENERATED BY THE DEALER, along with the dealer's Workshop Code (WSC) and the Importer number.

Does the vehicle have to be plugged into the VAS5051 to get the SKC? Is the SKC fixed to the ECU or will a new one be generated when required?

Use VAG-COM to read the VIN (17 digits) and Immo-ID (14 digits) from your car. Take these numbers to the dealer. Your car does not have to be connected to the dealer's tool. However, the Admin Screen of the dealer's VAS-5051 tool is a handy place to get the WSC and Importer Number that you also need for VAG-COM to be able to decrypt the 7-Digit SKC.

-Uwe-

Is the SKC hashed with the WSC, Import Number and Date? In which case does the SKC change or is it permanenet with each ECU?

<center><img src="http://www.ross-tech.com/vag-com/tour/screens/I_pin-skc_2081.gif"></center><p>The 7-Digit code is an encryption of the 4 digit code, using the WSC, the Importer Number and the Date as "seeds". The 7-digit code will change every day and from every dealer. But once you have it, you can use it forever with VAG-COM, since VAG-COM allows you to enter the date it was generated.

Hello

What if someone has a VAS 5051 at his home could he do anything with that...
Terry