New Tor version should help the network deal with increased traffic.
Sometimes a picture says more than a thousand words:
The graph shows the daily number of users of the
Tor
anonymity network over the past three years. As both the network and concerns over anonymity have grown, the usage has shown a slow but steady growth, with the occasional short peak. And then suddenly, in the third week of August this year, the number of users started to grow very quickly, resulting in a five-fold increase in barely two weeks.
Such a sharp increase cannot simply be explained by increased fears over surveillance, especially given that there was no noticeable increase in
Tor
usage directly following Edward Snowden’s
PRISM
revelations.
Some have suggested that the release of
PirateBrowser
, a web browser designed to circumvent censorship that uses
Tor
, was the reason for the huge increase, but this seems unlikely: the browser was released well before the number of
Tor
users started to grow, and it uses the
FoxyProxy
Firefox
plug-in – the use of which didn’t see such a huge increase.
A more likely explanation would be that a botnet is responsible for the increased use of
Tor
.
Botnets using
Tor
for command and control communications aren’t new. Neither are botnets that use
Tor
to hide the location of their nodes when performing a malicious activity: leaving comment spam on websites appears to be commonly done through
Tor
.
Researchers have been searching for evidence of such a botnet. Today,
Fox-IT
‘s Yonathan Klijnsma
writes
about a botnet that could well explain the surge in
Tor
users.
The malware he analysed isn’t new and is known as ‘Mevade’ or ‘Sefnit’, while to those running it may be known as ‘SBC’. Recently, coinciding with the increase in
Tor
users, it switched to
Tor
for its C&C communication. Both the size of the botnet and the particular
Tor
version used add to the belief that this is indeed what has caused the increase.
It is less clear what the purpose of the botnet is. Klijnsma suggests that the botnet – which he believes to originate in the former Soviet Union – may be used to load additional malware onto the system and that it (or parts of it) is offered for sale. He believes the ultimate motive is financial gain.
The latter may be a relief for many of
Tor
‘s supporters, who worried that this was a DDoS attack against the service itself, possibly by an entity that doesn’t like the idea of people using online anonymity. The fact that, rather uniquely, there has been no increase in
Tor
users in
Israel
had already provided fuel for conspiracy theories.
While a botnet consisting of millions of users is clearly harmful for the Internet as a whole, it is particularly harmful for
Tor
, whose four thousands nodes could barely deal with the increased traffic. In a blog post for the project,
Tor
‘s Roger Dingledine
explains
how some improvements to the protocol have been made that should help the network deal better with the increase in traffic.
The natural next step after the discovery of a large botnet would be to attempt to take it down. Normally this would involve shutting down, or taking over, the botnet’s command and control servers, but given their hidden nature, this will not be an easy task.
The anonymous nature of
Tor
also means that we will never be certain whether this particular botnet is responsible for the sharp increase in users. But assuming it is, I worry this isn’t the last we have heard of it. Hopefully security researchers will find a way to shut down the botnet and thus help the Internet in general, and
Tor
in particular.
Posted on 5 September 2013 by
Martijn Grooten
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