Nuclear terrorism is the currently hypothetical possibility that terrorists could obtain and use radioactive materials for destructive purposes. For instance, a "dirty bomb" (radiological weapon) detonated over a wide area could cost tens or hundreds of millions of dollars to clean up. Such a dirty bomb is emphatically not the same thing as a nuclear bomb -- it would merely consist of a radioactive material blown apart by a conventional bomb, for the purpose of causing radioactive contamination. Of course, a terrorist nuclear weapon would also be considered a type of nuclear terrorism.
Security experts across the world consider nuclear terrorism a plausible risk, and some leading analysts consider it only a matter of time before a dirty bomb or a nuclear weapon is detonated by terrorists in a major city. The impact of a dirty bomb would be primarily psychological -- several analyses have found that it would cause few casualties, though the mass panic could be incredibly destructive. A nuclear weapon, however, could kill anywhere between a few hundred and over a million people, depending on its yield and where it is detonated.
Several terrorist groups have expressed interest in obtaining the materials necessary to perpetrate nuclear terrorism, especially the enriched uranium that could be used to build a nuclear bomb. Osama bin Laden has called the construction of a nuclear bomb a holy mission for Al Qaeda. However, apart from this, there have been few concrete instances of evidence of extremists planning to obtain materials for nuclear terrorism.
In November 2006, the British intelligence organization MI5 warned that Islamic terrorists were planning to detonate a nuclear bomb in a UK city, but it is not known how sophisticated this planning was. In June 2007, Fox News claimed that the FBI told the press that Adnan Gulshair el Shukrijumah was responsible for planning the detonation of nuclear bombs in several US cities, but this has not been independently corroborated.
More tangibly, in November 2007 it was reported by 60 Minutes that burglars infiltrated the Pelindaba nuclear research facility near Pretoria, South Africa, but escaped without any enriched uranium. These burglars were never identified.