Thanks to Rodney Peterson of Educause for pointing this out:

U.S. cybersecurity chief abruptly resigns, cites frustration
By TED BRIDIS, AP Technology Writer
WASHINGTON (AP) The government’s cybersecurity chief has abruptly resigned after one year with the Department of Homeland Security, confiding to industry colleagues his frustration over what he considers a lack of attention paid to computer security issues within the agency.
Amit Yoran, a former software executive from Symantec Corp., informed the White House about his plans to quit as director of the National Cyber Security Division and made his resignation effective at the end of Thursday, effectively giving a single’s day notice of his intentions to leave.
Yoran said Friday he ”felt the timing was right to pursue other opportunities.” It was unclear immediately who might succeed him even temporarily. Yoran’s deputy is Donald ”Andy” Purdy, a former senior adviser to the White House on cybersecurity issues.
Yoran has privately described frustrations in recent months to colleagues in the technology industry, according to lobbyists who recounted these conversations on condition they not be identified because the talks were personal.

We’ve been harping on DHS and the Administration for not taking cyber security — especially cyber security R&D — seriously enough, but this still comes as a surprise.
More details as we figure them out.
Update: Rodney Petersen has more at the Educause blog on the suddenness of Yoran’s departure and its implications for Higher Ed.