Via a reader in Wisconsin (of course):

Airport security officers around the nation have been alerted by federal officials to look out for terrorists practicing to carry explosive components onto aircraft, based on four curious seizures at airports since last September. . . .

The seizures at airports in San Diego, Milwaukee, Houston and Baltimore included "wires, switches, pipes or tubes, cell phone components and dense clay-like substances," including block cheese, the bulletin said. . . .

"There is no credible, specific threat here," TSA spokeswoman Ellen Howe said Tuesday. "Don't panic. We do these things all the time."

NBC has more.

I suppose grated cheese, American cheese, and Cheez Whiz are safe. Just watch out for the "block cheese."