Government investigators smuggled liquid explosives and detonators past airport security, exposing a dangerous hole in the nation's ability to keep these forbidden items off of airplanes, according to a report made public Wednesday.

The investigators learned about the components to make an improvised explosive device on the Internet and purchased the parts at local stores, said the report by the Government Accountability Office. These covert tests were conducted at Transportation Security Administration checkpoints at 19 airports in March, May and June of this year...

But the investigators only tested one of TSA's 19 layers of security, said TSA spokeswoman Ellen Howe.

"While people think about us in terms of the checkpoints and they see us as the checkpoints, there's a lot more layers of security," she said. In addition to the checkpoints, TSA uses different technologies and has officials who check the validity of documents and observe people's behaviors throughout the airport. "Just because somebody gets through one layer doesn't mean they're going to get through all of the layers."

The report released Wednesday is a version of a classified report with sensitive information blacked out.