(CNN) One day, Michael Andrew Ryan sat down at a computer, hopped onto a hidden part of the Internet known as the dark Web, called himself "Gunrunner" and opened for business.

His international weapons operation offered anyone a virtual laundry list of weapons with brand names that have become disturbingly familiar:

To make these guns hard to trace, Gunrunner took off their serial numbers and shipped them to countries where buying these guns was difficult -- if not altogether banned by law.

And it was all happening under the noses of the residents of the sleepy little town of Manhattan, Kansas, population: about 56,000.

Gunrunner wasn't some dramatic villain like you might see in a Hollywood comic book thriller.

He was just a 35-year-old guy in America's Heartland, illegally exporting semi-automatic rifles, handguns and ammunition to Ireland, Scotland, Australia and England.

It just so happened that Ryan's online gun-selling operation got busted by the federal Bureau of Alcohol, Tobacco and Firearms.

"The fact that international firearms trafficking has reached Kansas shows the power of the Internet," said Acting U.S. Attorney Tom Beall in a statement.

As part of his June 6 plea agreement with prosecutors, Ryan admitted everything, according to court documents.

Ryan told a federal court he sold weapons on a website called BMR -- for Black Market Reloaded -- that was visible only to certain people who had access to specific software called Tor, according to court documents.

Now facing a maximum 10 years in prison and a $250,000 fine, a judge is scheduled to sentence Ryan on September 12.

A similar ATF bust in Alabama resulted in the sentencing of 48-year-old Michael Albert Focia last November. Focia's looking at 51 months in prison for using the dark Web to sell and ship "at least 32 firearms to people all over the world -- including Australia and Sweden," the U.S. attorney's office said.

The feds say they're shining more light on the dark Web to kill secret sites that terrorists or other criminals could use to build weapon arsenals.

The dark side

For those who are unaware of the dark Web — aka the deep Web or darknet— it's the hidden part of the Internet. It's not searchable on Google or other search engines.

And it's not just about guns. On the dark Web it's possible to buy or sell just about anything — including child porn or illegal drugs or stolen social security or credit card numbers, or even names on Ashley Madison accounts

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If you want to explore the dark side — you're going to need "special goggles" — software that lets you see the hidden sites.

Tor is a part of the dark Web that hosts many of these hidden sites. It's an acronym for "the onion router" because the addresses for Tor websites end in .onion.

You can download Tor software for free and start browsing the dark Web anytime. But don't say we didn't warn you: You may find yourself venturing into the Internet's Wild West, where users often operate by a different set of rules.

The dark Web even uses a different set of currency: Bitcoin, an anonymous form of money that isn't tied to banks or credit cards or any nation.

You may have first heard about the dark Web back in 2013 when the FBI shut down a popular marketplace site called Silk Road . It became an FBI target when nearly a million people were using it and sales rose to roughly $1.3 billion over about two years, the agency said.

'Like buying a bar of chocolate'

In 2014, a teenager named Liam Lyburd bought a handgun and other weapons materials on a dark website called Evolution and had them delivered to his home in Newcastle, England.

Lyburd was plotting a massacre.

Online, Lyburd used names such as "The Joker" and "I love my Anger." He posted disturbing messages on Facebook hinting about his terrible plans.

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A Facebook friend tipped off police about his posts, and authorities then raided Lyburd's home.

What police found inside his bedroom was jaw-dropping: a "kill bag" containing a Glock handgun, hollow tipped bullets, pipe bombs, boots, overalls and a mask.

During his trial, Lyburd told the court that buying the Glock online was "just like buying a bar of chocolate."

He was found guilty of plotting mass murder and sentenced to life in prison.

The Evolution site recently shut down, along with a few other dark Web gun marketplaces, including sites called Nucleus and Agora

How much gunrunning is going on?

As you might expect, it's hard to know exactly how large and widespread the online illegal weapons trade is.

According to a Carnegie Mellon University professor who researched the hidden Internet, it's comparatively small. Nicolas Christin told Fast Company that overall, illegal gun sales on the deep Web are tiny compared with other illegal Web trading — less than 3%.

By the way, it's entirely legal to buy guns online in the U.S. -- although the process is more complicated, depending on various factors.

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Nonetheless, the ATF said it's taking enforcement to a new level by creating an Internet Investigations Center aimed at combating illegal online gunrunners.

The center includes federal agents, legal counsel and investigators. Their job: track illegal online firearms trafficking and feed intelligence to agents in the field.

It's a gigantic task, which aims to hit a constantly moving target.