The Tor network is in danger of being swamped by criminals abusing its anonymity to hide an underworld of parasitic botnets, malicious command and control and 'darknet' markets, according to research from Kaspersky Lab.
Tor has long had its dark side but the scale of its use by criminals appears to have expanded quite rapidly in the last year. Kaspersky Lab had uncovered evidence of 900 services using Tor, said senior researcher Sergey Lozhkin, equivalent to 5,500 nodes (server relays) and 1,000 exit nodes (servers from which traffic emerges) in total.
A particular niche was the rise of underground markets that use Tor to hide their activity. "It all started from the notorious Silk Road market and evolved to dozens of specialist markets: drugs, arms and, of course, malware," said Lozhkin.
It was here that a growing number of forums dealing in stolen card data were finding a home, he said. Predictably, trade on these markets was now based almost entirely on Bitcoins, which can't be traced to individuals.
The figures Kaspersky has come up with our alarmingly high, depending on which way you look at it. Tor's own estimate of its relays runs at around 7,000 at any one time including bridges, with around 1,000 exit nodes; on that basis the number being abused by criminals seems high.
Techworld confirmed that these figures represent a cumulative total over time rather than those in use at one time. The scale of what is going on here is still very small next to what happens on the Internet itself but is clearly an abuse of a system designed to anonymise traffic in countries where legitimate Internet activity can get someone locked up.
"Hosting C&C servers in Tor makes them harder to identify, blacklist or eliminate. Although, creating a Tor communication module within a malware sample means extra work for the malware developers. We expect there will be a rise in new Tor-based malware, as well as Tor support for existing malware," said Sergey Lozhkin
Examples of Tor abuse are legion and include a recent Android botnet, the first ever discovered to be using Tor from that platform. Conventional botnets have also experimented with Tor. Probably the most infamous Tor parasite yet was the Silk Road market used to trade drugs, weapons, indeed anything illegal.
As for users, Tor's traffic has been prone to dramatic surges, including one in September 2013 when traffic rose from under 1 million users per day to well over five million in the space of a week. It has since dropped to around 3 million.