An unidentified flying object, or UFO, in its most general definition, is any apparent anomaly in the sky that is not identifiable as a known object or phenomenon. Such anomalies may later be identified, but depending on the evidence or lack of evidence, such an identification may not be possible generally leaving the anomaly unexplained. While stories of unexplained apparitions have been told since antiquity, the term "UFO" (or "UFOB") was officially created in 1953 by the United States Air Force (USAF) to serve as a catch-all for all such reports. It was stated that a "UFOB" was "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object." As originally defined, the term was restricted to those fraction of cases which remained unidentified after investigation, with USAF interest being for potential national security reasons and/or "technical aspects." (See Air Force Regulation 200-2.) During the late 1940s and through the 1950s, UFOs were often referred to popularly as "flying saucers" or "flying discs". The term UFO became more widespread during the 1950s, at first in technical literature, but later in popular use. UFOs garnered considerable interest during the Cold War, an era associated with a heightened concern for national security. Various studies have concluded that the phenomenon does not represent a threat to national security nor does it contain anything worthy of scientific pursuit (e.g., 1953 CIA Robertson Panel, USAF Project Blue Book, Condon Committee). Culturally, the phenomenon has often been associated with extraterrestrial life or government-related conspiracy theories, and has become a popular theme in fiction. UFOs have been subject to investigations over the years that varied widely in scope and scientific rigor. Governments or independent academics in the United States, Canada, the United Kingdom, Japan, Peru, France, Belgium, Sweden, Brazil, Chile, Uruguay, Mexico, Spain, and the Soviet Union are known to have investigated UFO reports at various times. UFOs are sometimes an element of conspiracy theories in which governments are allegedly intentionally "covering up" the existence of aliens by removing physical evidence of their presence, or even collaborating with extraterrestrial beings. There are many versions of this story; some are exclusive, while others overlap with various other conspiracy theories. In 1997, White House correspondent Sarah McClendon released an article about a group of government-employed scientists and technicians who state definitively that UFOs and aliens are real and are from other worlds. This group claimed that intimidation is still rampant and people are afraid to come forward with evidence that the phenomenon is genuine. "A group of government-employed scientists and technicians state definitively that UFOs and aliens are real and are from other worlds." McClendon stated that the Clinton administration had "many briefings on the subject." Laurance Rockefeller, well known for his comments on visitors from outer space, was the Clinton advisor on the subject. It is claimed that a number of other government officials, including Al Gore, have been privy to these briefings and documents.