Well crap - North Korea sets off another one

First hint was from the US Geological Survey:

Tectonic Summary
The shallow, magnitude 4.7 seismic event that occurred on 25 May 2009 at 00:54:43 UTC is linked to the claim of a nuclear test by North Korean officials. While the USGS cannot positively identify the seismic event as a nuclear test, it was shallow and located in the vicinity of the 9 October 2006 North Korean nuclear test (magnitude 4.3). Moreover, comparisons of the seismograms of the 9 October 2006 and 25 May 2009 events at individual seismic stations shows similar features, suggesting that the two events are in close spatial proximity and are the same type of source, although the more recent event is larger.

Next up - Voice of America confirms it:

North Korea Confirms 'More Powerful' Nuclear Test
North Korea says it successfully conducted an underground nuclear test that was more powerful than the country's first test some two-and-a-half years ago.

The country's official KCNA news agency reported that Monday's test was "part of measures to bolster [North Korea's] nuclear deterrent for self-defense."

South Korean President Lee Myung-bak convened an emergency security session over the test. The news also shook South Korean financial markets with the main share index falling nearly four percent.

Stormbringer talks about the military repercussions:

NORKORCOM NUCLEAR TEST
The question has been posed - "Is there a military option?"

There is always a military option. The question is not "Is there a military option?" Rather, the question is "Can we afford the price?"

Unfortunately, the primo window of opportunity to have launched an attack would have been BEFORE 9/11.

The fact remains we could still launch an attack on North Korea, although our resources are stretched mighty thin. Options include anything from commando raids - which are difficult to plan & coordinate - to air strikes, to full scale conventional military invasion - up to and including missile attacks.

Planning considerations must include the fact that the North Korean military is a fanatic organization that makes the Waffen SS look like Boy Scouts. They will fight to the bloody end. To complicate matters, the entire country is in hardcore defensive posture (beaucoup anti-aircraft artillery, anti-helicopter cables strung between mountains, minefields galore, and beach defenses a la Atlantic Wall).

The consensus was that the first test was a partial dud -- there is a specific range of yield that should have been expected for a bomb of that type and the test was lower than it should have been. In a few weeks, we will have more information.