Designs that could be used to make a gun using a 3D printer have been removed from the US website that published them earlier this week, after a US State Department request.
Cody Wilson who runs defcad.org is reported to have received a letter from a State Department official, saying he had released "technical data" without authorisation.
The move may have violated arms export regulations.
Concerns about the gun centre on the fact that it may not be easily detectable by metal detectors, because it contains minimal amounts of metal.
The Undetectable Firearms Act in the US outlaws the manufacture, import, selling, shipment, delivery, possession, transfer, or reception of any firearm that is not detectable by walk-through metal detectors.
It outlaws major components that do not generate an accurate image by airport X-ray machines.
Earlier this week, Mr Wilson sparked controversy by publishing the designs for the Liberator, a simple gun made of plastic.
The website also featured a video of the weapon being fired.
Between the time they were published and their removal at the State Department's insistence, the designs had been downloaded more than 100,000 times.
It is reported that despite their removal, copies of the designs are now freely circulating on the internet.
A note posted on the top of the Defcad website reads: "Defcad files are being removed from public access at the request of the US Department of Defense Trade Controls.
"Until further notice, the United States government claims control of the information." it said.