matthew olsen is director of the national counterterrorism center.told a senate hearing that the militants are exploiting "increasingly permissive security environments in iraq," and he warned other al qaeda affiliates are spreading. >> the threat level, as we look at the threat, is more disbursed geographically. the threat is... has moved out from the afghanistan-pakistan border region to broad swaths of areas that are largely ungoverned across north africa and the middle east. so, in some ways, it has... it has become more significant from a geographic perspective and more complicated from an intelligence perspective. >> woodruff: still, olsen said the threat of another 9/11-style attack on the u.s. is lower than it was in 2001. the nominee to chair the federal reserve is defending the central bank's stimulus efforts. janet yellen faced her senate confirmation hearing today. she said the economy still needs help, and she gave no indication of when the fed might curtail its stimulus program. there'll be more on the yellen hearing later in the progra