The TSA's evolving list of banned objects has drawn mixed reaction from travelers.

"Let's allow knives on board, but you are not allowed a bottle of water, or a bottle of baby food," wrote one CNN.com reader.

Another seemed to take a more positive view: "I almost had my kids' safety scissors confiscated from their little activity kit. Yay for this sensible decision."

Commenter Jose L. Reynoso was more skeptical.

"Yeah sure one man against a bunch of others is no match but, what if ten men carrying knives and bats plot to take over? Wouldn't a massacre be obvious?" Reynoso wrote.

A more flexible aviation security system?

A country's security services need to be collecting intelligence on potential terrorists way before passengers board an aircraft, said Bloom. And any airport's security team needs to have flexible and layered screening in place to be able to adjust its processes for high-risk individuals.

"The threat is ever-changing."