I don't "know"; however, I "suspect" that this is an example of some group flexing their collective muscles to test out a number of processes. Who they are and where they come from is unclear.
I also suspect that these are probing operations, designed to tested operational capacity of both sides. Specifically, their ability to conduct the attack and the capacity of companies and agencies to respond appropriately. We may see a few more of these, possibly in the not too distant future; and then possibly even a full scale attack.
I somehow doubt that this is the work of script kiddies; it seems to be too focussed and determined for that. I'm betting that the more senior members of the security community are privately very worried indeed.