The so-called "dark web," a shadowy part of the internet you haven't likely visited and won't find using Google, has become an online haven for anyone looking to buy or sell drugs, weapons or other illegal goods. And it's leaving law enforcement stumped.

One of the most well-known examples is a website similar to eBay called Silk Road, where, instead of electronics and household goods, users buy and sell street drugs such as ecstasy and magic mushrooms.

Like many sites on the dark web, Silk Road isn't indexed by commonly used search engines and is difficult for everyday internet users to access. It's also been operating with relative impunity for the past two years despite reaching sales of $1.2 million US per month in 2012, according to one estimate by Nicolas Christin, associate director of the Information Networking Institute at Carnegie Mellon University.

In recent days, Silk Road has reportedly come under repeated denial-of-service attacks, which involve overloading a site with web traffic. While there has been speculation that law enforcement may be behind those attacks, many other observers point to the possibility of a virtual turf war in the growing online market for illicit drugs.

A new competing site called Atlantis, which offers cheaper prices for drug dealers to list their goods, is trying to capitalize on Silk Road’s misfortune. As one announcement on the popular social news site Reddit says: now is the "Perfect Time to check out the new Atlantis Marketplace," with Silk Road out of the picture.

Criminal haven

Drugs aren't the only illicit goods bought and sold through such obscure websites. Stolen credit card information, malicious software, guns and even explosives are on offer for the right price.

"Unfortunately a lot of the stuff we deal with is child pornography," said Det. Sgt. Eugene Silva, who is with the technological crimes unit of the Waterloo Regional Police.

Investigating child pornography sites can be difficult because they tend to relocate across international borders, hopping from one server to another to elude law enforcement officials, he said.

"It could be in some Asian country today, and in a week’s time it’s somewhere in Russia or the Netherlands," Silva said.

Police scouring the dark web as part of criminal investigations have the added hurdle of dealing with the Tor network, which is a technology that Silva admits has stymied his three-person unit.

The Tor network operates on the ".onion" domain and allows users to surf the web with much greater anonymity, making it harder to track a person's online communication or which sites they visit. Sites like Silk Road also tend to use virtual alternatives to conventional money like Bitcoin, which can be more difficult to trace.

If a suspect is using the Tor network, Silva said, he and the two detectives he commands will try to track them elsewhere on the web by searching for clues that might help identify the person on Facebook, Twitter, or other social media sites.

Bright side of anonymity

But the dark web isn't all bad, said Chester Wisniewski, senior security advisor with British-based internet security firm Sophos.

Wisniewski acknowledged that criminals use secretive websites for all kinds of nefarious ends, but he points out that other groups including political dissidents and journalists also benefit from the anonymity the dark web offers.

"You start thinking about the people who are trying to report on what’s happening with [President Bashar] al-Assad in Syria," he said by phone from New York.

"If you’re on the ground there as a journalist or even as a civilian blogger, and you want to get the word out about whether the government really is using poison gas on its own citizens, that is a very difficult thing to securely communicate inside of a war-torn country or a dictatorship, without knowing that you’re going to lose your own head," he said.

Being able to communicate anonymously can help elude pro-government hackers trying to root out anyone who is sympathetic to the Syrian opposition, and protect journalists trying to report on the war.

Then there are those in conflict-free countries who simply use the dark web because they want to do whatever they can to protect their online privacy and minimize the chances of being spied on, Wisniewski said.

"There really isn’t anything wrong with that," he said. "There’s compelling need for it."