By Susannah Cullinane

(CNN) -- Not long ago, it was the stuff of science fiction, but now US officials and lawmakers are grappling with a new reality -- the ability for citizens to print firearms at home.

A gun rights group that posted plans for 3D guns blocked downloads from its website Tuesday after a federal judge sided with states that the postings could help criminals and terrorists manufacture such weapons.

While Judge Robert Lasnik's ruling didn't order the plans taken down, it temporarily blocked a settlement that Defense Distributed, a Texas-based gun rights organization, and the federal government reached in June that made it legal to post 3D printable gun plans online.

"This is a nationwide ban. ... It takes us back to a period of time before the federal government flipped on their policy regarding these 3D ghost guns," Washington Attorney General Bob Ferguson said.

So what's the controversy all about?

What are 3D-printed guns?

The process of 3D printing uses computer-created digital models to create real-world objects -- everything from simple chess pieces to more complex objects such as functioning clocks. The printers follow the shape of the model by stacking layer upon layer of material to make the objects.

Do-it-yourself firearms such as the Liberator have been nicknamed "ghost guns" because they don't have serial numbers and are untraceable.

The Defense Distributed website would have allowed people to download plans for building the Liberator as well as files for an AR-15 lower receiver, a complete Beretta M9 handgun and other firearms. Users could share their own designs for guns, magazines and other accessories. Defense Distributed founder Cody Wilson said the site has disabled downloads until he reviews the judge's order.

The high-end 3D printers needed to make such weapons cost thousands of dollars and may be too expensive for most people. But that doesn't ease the concerns of those who think guns made from 3D printers are a bad idea.

What sparked the controversy?

In May 2013, Defense Distributed posted to YouTube what appeared to be the first video of the live firing of a handgun created with a 3D printer.

The 53-second video showed a single shot being fired from the Liberator, a plastic handgun that, with the exception of its metal firing pin, was assembled from parts made with a 3D printer, according to Defense Distributed.

The single-shot pistol was made almost entirely out of ABS plastic -- the same material from which Lego blocks are made.

Wilson -- then a 25-year-old law student -- posted designs for the gun online so that other people could duplicate it.

Defense Distributed began a self-described Wiki weapon project in 2012 but until its May 2013 video, had only reported being able to make plastic, interchangeable parts for firearms -- not entire weapons.

Wilson has emerged as the face of the group based near Austin, Texas, although many of its members, including the owners of the 3D printer the group uses, have chosen to remain anonymous.

Why did the US government intervene?

A few days after Defense Distributed posted its instructions for making a gun, the US State Department sent a three-page cease-and-desist letter to Wilson demanding that the group remove them from its website.

It accused Wilson of potentially breaching International Traffic in Arms Regulations, which regulate the export of defense materials, services and technical data.

In essence, officials said, someone in another country that the United States doesn't sell weapons to could download the material and make guns.

Wilson complied but said the files already had been downloaded 1 million times. He sued the federal government in 2015, citing his right to free speech.

Defense Distributed reached a settlement with the US government last month that allowed it to post 3D-printable gun plans online starting August 1, 2018. The settlement says Wilson and Defense Distributed can publish plans, files and 3D drawings in any form and exempts them from the export restrictions. The government also agreed to pay almost $40,000 of Wilson's legal fees and to refund some registration fees.

A State Department spokesman told CNN the settlement came after a national security analysis that determined "certain firearms and related items that are widely available for commercial sale, and technical data related to those items, is of a type that does not offer a critical military or intelligence advantage to the United States."

The spokesman added that the US government is reviewing plans to transfer oversight of firearm exports from the State Department to the Commerce Department, which would eliminate the International Traffic in Arms Regulations requirements that had initially prevented the uploading of the gun production plans.

The Trump administration said it supports an existing law they say makes it illegal to own or make homemade plastic guns, a White House official said Tuesday after President Donald Trump tweeted that the availability of the firearms "doesn't seem to make much sense!"

"The President is committed to the safety and security of all Americans; he considers this his highest responsibility," deputy press secretary Hogan Gidley said. "In the United States, it's currently illegal to own or make a wholly plastic gun of any kind, including those made on a 3D printer."

What other legal challenges are in play? On Friday, the State Department posted a notice temporarily modifying the US Munitions List to exclude the "technical data" at the center of the lawsuit, paving the way for its legal publication.

Gun control groups lost an emergency bid the same day to block Defense Distributed from posting its instructions online.

The move to try and intervene in the case by three leading gun organizations -- the Brady Campaign to Prevent Gun Violence, Everytown for Gun Safety and Giffords, a group founded by former US Rep. Gabby Giffords -- was a last-ditch attempt to thwart Defense Distributed ahead of the expected online release.

In a filing, a federal judge in Texas faulted the groups for failing to prove they were actually legitimate parties to the case.

State attorneys general have been fighting to keep 3D-printed guns out.

At an emergency hearing held over the phone Sunday, Pennsylvania Attorney General Josh Shapiro asked a judge for a restraining order that would block Defense Distributed's website from being accessible in his state.

At the hearing, Defense Distributed agreed to block Pennsylvania IP addresses for a few days until a more formal hearing could be held.

Pennsylvania isn't the only state trying to bar access to 3D-printed guns. Washington state Attorney General Bob Ferguson announced Monday he is leading a lawsuit in eight states and the District of Columbia to block a court action that would let people download plans for untraceable 3D-printed weapons. This lawsuit is being filed in federal court in Seattle.

Meanwhile, 21 state attorneys general sent a letter to Secretary of State Mike Pompeo and Attorney General Jeff Sessions, urging the government to withdraw from the settlement.

What about lawmakers?

In December 2013, a federal law requiring that all guns be detectable by metal screening machines was extended for another 10 years.

The law prohibits guns that don't contain enough metal to trigger screening machines commonly found in airports, courthouses and other secure areas accessible to the public.

Plastic gun designs got around this restriction by containing a metal block that could be removed and that the firearm could function without.

In June, Sen. Bill Nelson, D-Florida, introduced a bill in the Senate that would amend the Undetectable Firearms Act to prohibit firearms that do not have a major component that can be detected at airport security screening.

New York Gov. Andrew Cuomo announced a series of actions Tuesday to prevent the distribution of the 3D gun designs. Cuomo issued a cease-and-desist letter to Defense Distributed to block the distribution of designs for 3D guns in New York. The governor called the impending release "reckless."

Cuomo also directed state police to issue a notice reminding New Yorkers that manufacturing firearms defined as assault weapons is illegal in New York.

What are the arguments against the guns?

Critics fear the DIY guns could easily fall into the wrong hands and create safety concerns because they'd be invisible to metal detectors.

Top prosecutors in New York and Los Angeles blasted the settlement as an "unconscionable mistake."

"No one is safer if criminals can print untraceable guns on demand," Los Angeles City Attorney Mike Feuer and Manhattan District Attorney Cyrus Vance Jr., co-chairs of the Prosecutors Against Gun Violence group, said in a statement.

"Allowing this exemption from federal rules would be an unconscionable mistake, making it all-too-easy for anyone with a dangerous history -- including terrorists and domestic abusers who cannot pass a background check -- to download files and print a functional gun with 3D printers available to any consumer. This decision undermines the critical public safety laws that prosecutors enforce day in and day out," the statement said.

Guns from 3D printers will make it easier for terrorists and people who are too dangerous to pass criminal background checks to get their hands on guns, said Avery Gardiner, co-president of the Brady Campaign to Prevent Gun Violence.

Actor and activist Alyssa Milano wrote that the settlement meant "felons, domestic abusers, terrorists, those adjudicated too mentally ill to own guns and any other person unable to legally purchase firearms will be able to print one at home."

"It is not hyperbole to say that this could mean the end of our ability to have meaningful gun violence prevention in America," Milano said in an opinion piece for CNN published Monday.

How effective are the guns?

In 2013, the Bureau of Alcohol, Tobacco, Firearms and Explosives made public tests it has done on the Liberator.

One gun made using a plastic called ABS-M30 fired a .380-caliber round without failing all eight times when it was tested, ATF officials said, describing it as "a lethal weapon."

Another pistol made from a plastic called VisiJet didn't perform as well, with video showing it exploding into a dozen plastic shards when fired.

In Britain, researchers at Warwick University were involved with police ballistic testing of the weapons in 2014. The university said, "The results of the tests have shown that due to the variability in printers, software and materials the results of printing such items are highly unpredictable with the implication that if someone were to produce items the result could be complete failure and injury to the user."

German-based 3D printing magazine All3dp said police testing showed a gun from a 3D printer "could endanger the shooter as much as anyone else."

"A firearm produced with ABS material could break apart or even potentially explode in the hands of the user when fired. Softer PLA will likely cause the parts to bend or deform after firing," it said, referring to a flexible 3D printing material.

So why bother fighting to make them legal?

It's about the right to bear arms, its advocates say.

On Monday, Defense Distributed founder Wilson tweeted, "I am now being sued by at least 21 state attorneys general. If you want your Second Amendment online, THIS is the fight."

Wilson has made no secret of his disdain for the US government in particular and all governments in general. (Defense Distributed makes and sells components with names such as the Cuomo and the Pelosi named after politicians such New York's governor and the House minority leader who support gun control efforts.)

"For me, it's important as a symbolic political statement," Wilson told CNN in 2013. "And that statement is something like, 'No, the future we imagine is one of personalized manufacture and access to objects. ... In this future, people will be able to make guns for themselves.'

"That was already true, but now it's been demonstrated in yet another technology."

For Wilson and his supporters, the ability to build unregulated and untraceable guns will make it much harder, if not impossible, for governments to ban them.

Alan Gottlieb, a founder and vice president of the Second Amendment Foundation, told CNN's "Cuomo Prime Time" that it was a matter of applying the First Amendment to protect citizens' Second Amendment rights. He said some communities are losing access to firearms sellers because of local laws.

"If you're allowed to own a firearm in your own home, you should be able to make the firearm in your own home if you can't buy one locally because of crazy restrictions," he said.

What about the rest of the world?

When Defense Distributed first made the plans available in 2013, Forbes quoted one of the group's developers as saying they had been downloaded in countries, including Spain, Brazil, Germany and the UK.

Britain's Mail on Sunday newspaper later reported that two of its reporters had taken a Liberator gun on the Eurostar train from London to France.

Britain has strict gun laws that include certification for gun owners and their weapons. The UK's Home Office has made it clear that "the expression 'firearm' in the 1968 (Firearms) Act means a lethal barrelled weapon of any description, or component part of such weapon, from which any shot, bullet or other missile can be discharged," including 3D weapons.

A 2014 analysis of the EU Directive on Firearms prepared for the European Commission said: "As for 3D printing, in EU countries the manufacture of firearms and components with this new technology is not an issue as in the USA, since all firearms' manufacturing is subject to government permission. Furthermore, it is much easier to illegally manufacture parts of weapons by means of traditional machines which are in free circulation, cheaper and much more precise. ..."

Meanwhile, an Australian briefing paper on 3D printing and crime prepared by researchers at the Queensland University of Technology said: "In some jurisdictions, it may be easier to obtain a traditional firearm (either legally or illegally) than self-produce a 3D printed gun. It may be challenging for users without technical expertise to actually use 3D printers, especially cheap plastic printers. However, it could be easier to buy a 3D printer and print a firearm in countries that have strict guns laws or are geographically isolated (for example, Australia)."