The most recent finding concerns a complex, heavily encrypted networking program called the Invisible Internet Project, or I2P. Used to send messages and run websites anonymously, I2P ships along with the specialized operating system "Tails," which former U.S. spy contractor Snowden used to communicate with journalists in secret.
Though a core purpose of I2P is to obscure the Internet Protocol addresses of its roughly 30,000 users, anyone who visits a booby-trapped website could have their true address revealed, making it likely that their name could be exposed as well, according to researchers at Exodus Intelligence.
"People shouldn't trust something wholeheartedly just because Snowden says," Exodus Vice President Aaron Portnoy told Reuters. "Generally, we assume the things we can find, others can find."
Tails launches from a DVD or USB stick and is designed to maintain privacy even when a computer or network has been hacked.
Much more than I2P, Tails relies on Tor, the better-known anonymity system that it uses for all software connections to the Internet. But leaks in the past year have shown that Tor is also a major target for the U.S. National Security Agency and others, and researchers at Carnegie Mellon University said they could have identified hundreds of thousands of Tor users.
Those researchers planned to detail their technique next month at the security conference Black Hat. After Tor developers complained to Carnegie Mellon, the university told Black Hat to cancel the talk.
Tor programmer Roger Dingledine conceded that the researchers had found a flaw, and he said his team was now working to fix it before any public disclosure exposes dissidents and other types of users on Tor to greater risk of attack.
The I2P flaw will likewise be fixed. A spokesman for the I2P project said the group of developers was still analyzing the Exodus report.
Tails did not respond to an email seeking comment. It was not clear how many Tails users would have been vulnerable without Exodus' cooperation, since the I2P application does not launch automatically when the operating system is opened.
Exodus is one of a dozen or more companies known to sell secret security flaws to intelligence agencies, law enforcement and other customers in a controversial marketplace.
NO SYSTEM IS FAILSAFE
But in this case, Exodus alerted I2P and Tails to the problem and said it would not divulge the details to customers until the problem has been fixed. Portnoy declined to say what the company would do if a government client asked him to find a similar flaw in the future.
The Tails and Tor episodes show that no anonymity system is failsafe, Portnoy said, and those in jeopardy should focus on compartmentalizing their efforts so that a single breach would not expose everything about them.
"Tor works for most purposes, but a determined adversary will always find a way," he said.
In one such high-stakes case, the FBI used a flaw in a Firefox Web browser that came bundled with Tor to identify a man suspected of hosting child pornography, according to Irish media reports.
Leaked NSA documents show that the NSA logged the IP addresses of many Tor users and may have scanned emails for users living outside of the United States and its four closest intelligence allies, German media reported this month.