The country's Homeland Security chief is warning authorities to be vigilant, knowing that one of the hardest types of terror attack to pick off - the lone-wolf attack - could be inspired by the upcoming anniversary of the death of Usama bin Laden.
FOX Chief Intelligence Correspondent Catherine Herridge reports in our ongoing series on national security:
While there is no specific or credible intelligence pointing to an attack, the law enforcement bulletin says homegrown terrorists - the so-called lone wolf - may see next week's anniversary as the ideal time to retaliate for bin Laden's death. The Homeland Security Secretary, Janet Napolitano, testified on Capitol Hill Wednesday.
(Napolitano) "When I say terrorism continues to evolve, that's one of the evolutions that we're seeing. Radicalization, radicalization to the point of terrorist violence."
According to the Congressional Research Service, there have been more homegrown cases in the last two-and-a-half years than in the first eight years after 9/11.
In Washington, Catherine Herridge, FOX News Radio.