The FBI and Department of Homeland Security are issuing a warning that terrorists may be renting small planes and filling them with explosives for possible attacks. The bulletin says, "Violent extremists with knowledge of general aviation and access to small planes pose a significant potential threat to the Homeland."

While there's no "credible" information about a threat, the authorities are concerned because, according to CNN, "as recently as early 2011, al Qaeda was considering options for targeting aviation 'possibly believing such operations would have a greater impact than other types of attacks.' Among the strategies al Qaeda members have discussed are using a private aircraft to carry explosives, finding a Western operative who could easily travel to the United States or Europe to get flight training or renting private planes for attacks, 'believing supervision would be lax due to the large number of private aircraft.'"

Police Commissioner Kelly told WCBS 2 that while there's no credible threat, the NYPD has increased security, "We’re concerned about it. We of course are concerned particularly because bin Laden spoke about it twice in the notes that were recovered.”

As it happens, just days ago Homeland Security Secretary Janet Napolitano said she didn't think Al Qaeda had any 10th anniversary attack plans but also added you never know.