It is not illegal to access the dark Web, but transactions there - such as buying stolen information, hacking tools and drugs - are, said lawyers.
The dark Web resides in online spaces that popular browsers cannot enter easily, and it tries its best to keep it that way.
Users have to install special software on their computers to access websites that may disappear as suddenly as they pop up. Access to forums and marketplaces on the dark Web may require the user to be a regular contributor or referred by someone trusted by the circle.
"The dark Web is a special club," said Mr Azly J. Nor, 30, who runs tech consultancy Blackwilder and has used the dark Web for its encrypted communications.
Website addresses are posted in these forums that are open to selected members, he added.
The addresses add another layer of security: They are garbled numbers and letters. For example, Silk Road, a now-defunct marketplace for drugs, was at http://silkroadvb5piz3r.onion
Dark Web sites are not indexed by popular search engines, and they also do not have links that transport users in and out of them.
Currently, the most popular way to access the dark Web is through The Onion Router (Tor), an Internet privacy service that can decrypt dark Web sites - a function that other browsers such as Chrome, Internet Explorer and Safari do not have.
Users who go through the trouble to get Tor do so to stay anonymous. Tor started as a project that allows whistle-blowers who live in oppressive states to share information anonymously.
Tor hides its users' identities by sending data through three other servers before the message reaches its destination. Speed is sometimes slower as a result, said Mr Azly.
But the anonymity that Tor provides also attracts people who want to buy and sell illegal products such as drugs, weapons and stolen credit card details in a digital black market. Under Singapore's law, it is illegal to buy these illicit items online.
Before the authorities in the United States took down Silk Road in October 2013, it was known as the Amazon for drugs. Another digital black marketplace called AlphaBay was also shut down in July this year.
Payments are made using digital currency bitcoin.
According to technology magazine Wired, AlphaBay, with about 300,000 listings of contraband items, made between US$600,000 (S$803,770) and US$800,000 a day.
Aw Cheng Wei