Last month, U.S. authorities arrested Ross William Ulbricht and charged him with running an online marketplace for a cornucopia of illegal goods and deals. That online bazaar was called The Silk Road, which, like its fabled namesake, offered visitors just about anything they desired.

The arrest has thrown light on two disturbing elements of the Internet — the existence of the so-called Deep Web, a massive virtual world that is not visible to most Web users or search engines, and the use of Bitcoin, a rapidly expanding digital currency that allows for anonymous transactions.

These revelations are a reminder that despite fears of living in a surveillance state, substantial parts of the digital world remain unobserved and unregulated — perhaps dangerously so.