DENVER -- Security officials at Denver International Airport have started random swabbing of some passengers' hands and carry-on bags as part of a new "Explosives Trace Detection" screening.

The screening was expanded at airports nationwide in response to a failed Christmas Day bombing attempt by a Nigerian man who to tried to ignite explosives concealed in his underwear on an Amsterdam-to-Detroit flight, the Transportation Security Administration said.

DIA began doing the explosive-detection screening this week. Read about how the Explosives Trace Detection technology works and the expansion of screening at airports nationwide.

At security checkpoints, some passengers are randomly selected to have their hands or carry-on items swabbed, and then the swab is run through a computer-analysis machine that scans for explosive residue.

To ensure that passengers will not be exposed to flu or cold germs, the TSA said the screening swabs are disposed of after each use.