Joseph Menn, Dustin Volz and Mark Hosenball

Obama administration officials briefed key congressional staffers last week about a secret court order to Yahoo Inc (YHOO.O) that prompted it to search all users’ incoming emails for a still undisclosed digital signature, but they remain reluctant to discuss the unusual case with a broader audience.

Executive branch officials spoke to staff for members of the Senate and House of Representatives committees overseeing intelligence operations and the judiciary, according to people briefed on the events, which followed Reuters’ disclosure of the massive search.

But attempts by other members of Congress and civil society groups to learn more about the Yahoo order are unlikely to meet with success anytime soon, because its details remain a sensitive national security matter, U.S. officials told Reuters. Release of any declassified version of the order is unlikely in the foreseeable future, the officials said.