This is the official Microsoft SP3 blocker toolkit. You download it,
run the file, and unpack it somewhere. Then open a command prompt
window, go to the folder where you unpacked it, and run the .cmd file
with a /B to make the blocking effective.
The previous service pack is *only* supported for twelve months after
release, so you will probably want to update at that time. Otherwise
you will not get security updates after twelve months.