A company that supplies controversial passenger-screening machines for U.S. airports is under suspicion for possibly manipulating tests on privacy software designed to prevent the machines from producing graphic body images.

The Transportation Security Administration sent a letter Nov. 9 to the parent company of Rapiscan, the maker of backscatter machines, requesting information about the testing of the software to determine if there was malfeasance.

The machines use backscatter radiation to detect objects concealed beneath clothes. But after complaints from privacy groups and others that the machines produce graphic images of passenger's bodies, the government ordered the machines be outfitted with privacy software by June to replace the invasive images with more generic ones that simply show a chalk-like outline of a body.

While L-3 Communications, the maker of another brand of scanners used in airports, successfully developed the privacy software for its machines, Rapiscan was having problems with its software, according to Bloomberg.

The testing of the software, done earlier this year to determine if it met privacy requirements, was conducted by a third party, so it's not immediately clear how Rapiscan might have manipulated the tests.

At a hearing on Thursday before the House Transportation Security Subcommittee, Chairman Mike Rogers (R-Alabama) asked John Sanders, assistant administrator for TSA's office of security capabilities, this very question. Sanders replied obliquely that "before [a test] gets underway, we might believe the system is on one configuration when it's not in that configuration."

Sanders said that TSA has no evidence yet that the vendor did manipulate the tests, but is looking into the matter.

“At this point we don’t know what has occurred,” Sanders said. “We are in contact with the vendor. We are working with them to get to the bottom of it.”

The vendor has denied any wrongdoing.

“At no time did Rapiscan falsify test data or any information related to this technology or the test,” Peter Kant, an executive vice president with the company, told Bloomberg.

DHS has spent about $90 million replacing traditional magnetometers with the controversial body-scanning machines.

Rapiscan has a contract to produce 500 machines for the TSA at a cost of about $180,000 each. The company could be fined and barred from participating in government contracts, or employees could face prison terms if it is found to have defrauded the government.

It's not the first time Rapiscan has been at the center of testing problems with the machines. The company previously had problems with a “calculation error” in safety tests that showed the machines were emitting radiation levels that were 10 times higher than expected.

It turned out the company's technicians weren't following protocol in conducting the tests. They were supposed to test radiation levels of machines in the field 10 times in a row, and then divide the results by 10 to produce an average radiation measurement. But the testers failed to divide the results by 10, producing false numbers.

A recent Wired.com three-part series examined the constitutionality, effectiveness and health concerns of the scanners, which were never tested on mice or other biological equivalents to determine the scanners’ health risks to humans.