A security researcher has abruptly cancelled next month's scheduled unveiling of a privacy device designed to mask Internet users' physical locations. It's a move that has both disappointed privacy advocates and aroused suspicions.

Ben Caudill, a researcher with Rhino Security Labs, took the unusual step of saying he no longer plans to release the software or hardware schematics for his so-called ProxyHam box. He said the devices already created have been destroyed. Caudill has offered no explanation for the killing of the project, but he has reportedly ruled out both intellectual property disputes and Federal Communications Commission licensing concerns.

That has left some people to speculate a secret government subpoena known as a National Security Letter is at play in the decision to kill the project. That speculation seems unlikely because NSLs are a very specific legal process typically served on e-mail providers, phone companies, or the like for specific information, Electronic Frontier Foundation General Counsel and Deputy Executive Director Kurt Opsahl said.

"It's not clear to me how that could possibly map to the product you described," he said after Ars explained how ProxyHam worked. "It's not a catch-all letter by which the government can obtain any action for anybody."

The ProxyHam device was able to mask the location of an Internet user by broadcasting on a 900MHz radio frequency so the owner could connect from up to 2.5 miles away from the source of the Internet connection. As a result, even if someone tracked down the location of an IP address, the user wouldn't automatically be discovered. The box was billed as using open-source software and requiring less than $200 in hardware. It was scheduled to be the topic of a now-canceled talk at next month's Defcon hacker conference in Las Vegas.

Other speculation on why the project was cancelled holds that ProxyHam was never the break-through device some journalists and privacy advocates made it out to be. ProxyHam, according to Errata Security CEO Rob Graham, was little more than the combination of a Raspberry Pi computer and a $125 900 MHz bridge from a company called Ubiquiti Networks, with some software that made them interoperate.

"I don't know why the talk was canceled," Graham wrote in a blog post published Monday afternoon. "One likely reason is that the stories (such as the one on Wired) sensationalized the thing, so maybe their employer got cold feet. Or maybe the FBI got scared and really did give them an NSL, though that's incredibly implausible."

Whatever the reason for the cancellation, it wouldn't be hard for someone else with expertise in hardware to create a box that does exactly what Caudill described. So far, there's no word of anyone offering to sit in for Caudill.