With the confirmed death of Osama bin Laden, one of the masterminds behind the infamous September 11th terrorist attacks, authorities are stepping up security and calling for extra vigilance in the face of possible retaliatory terrorist attacks.

A week before bin Laden's death was announced by President Barack Obama, leading to a triumphant gathering of cheering and celebrating crowds outside the White House in Washington D.C. and at Ground Zero, AFP-- the Paris-based, French news agency-- reported the contents of WikiLeaks documents bearing an ominous message from Khalid Sheikh Mohammed, the Al-Qaeda operative who originally conceived the plot to hijack planes and crash them into military and civilian targets.  While interrogated in Guantanamo Bay prison, the leak revealed, Khalid Sheikh Mohammed warned that if Osama bin Laden was captured or killed, it would unleash a "nuclear hellstorm" of retaliation against NATO countries, including a nuclear bomb that Sheikh Mohammed claimed had been hidden by Al-Qaeda operatives somewhere in Europe.

His comments should be taken with some degree of healthy skepticism as they were extracted by means of so-called "enhanced interrogation" techniques that put him under extreme physical duress, including the controversial waterboarding technique that some have called torture.  In addition to the hidden nuclear weapon, Khalid Sheikh Mohammed claimed that he had set up cells to attack London Heathrow Airport in 2002 and in late 2001, he had set up cells to attack "the tallest buildings in California" with hijacked planes, reports German weekly Der Spiegel, citing the WikiLeaks Guantanamo documents

It wouldn't be the first time the public learned that California, America's largest state by population and gross domestic product, had been named as a target for terrorist activity. In 2005, the Bush Administration disclosed the details of an Al-Qaeda plot to crash a hijacked plane into the U.S. Bank Tower (formerly known as the Library Tower) in Los Angeles.

In a poll published online Monday, CNBC asked participants if they felt safer as a result of Osama bin Laden's confirmed death at the hands of a U.S. special operations team. Late Monday night, with over 10,000 participants in the unscientific Internet poll, a scant 28% of respondents said the news of bin Laden's death made them feel safer, while an astonishing 72% said that the news did not make them feel safer.

Public officials, including CIA Director Leon Panetta, are warning that an attempt by Al-Qaeda to avenge Osama bin Laden's death is almost certain, and encouraging citizens to remain alert and vigilant, even as U.S. intelligence and defense step up security measures to keep Americans safe.  While it is extremely prudent to remain careful and vigilant, it is also important for Americans to live their lives free from the terror that groups like Al-Qaeda hope to elicit. When California was on alert for terrorist attacks in 2002, Governor Gray Davis had these wise words to offer in an interview with CNN: "I just want Californians to go on with their lives."