Great to see the Dev's releasing a fix so quickly...as with all experimental software and running a new protocol PoWT things will happen unexpectedly. I believe all the testing on the testnet would of not shown this bug because the amount of hashing power and users that are being thrown at the network. Every software release from Bitcoin to Ethereum have had bugs similar to this...comes with the game. We do have a great product here and when things get fixed quickly it shows we have competent, capable developers.
So Doug, Pat and David...was this an attack by a bad actor or just a bug? Just for clarification ;-) As you guys always seem to be attacked at some point....
Already answered
"Basically the difficulty adjustment was set too aggressive such that when an aberrant block timestamp came in the difficulty adjustment was too severe for the protocol to allow, so the work from that point on was not accepted."