The world's largest botnet Zeus has had its traffic disrupted after an international effort to shut down a rogue ISP, which is responsible for controlling large numbers of computers infected with data-stealing code is down for the moment. But a series of reconnections may revive Trojan, according to security researchers.
Troyak, which is believed to be based in eastern Europe, was knocked offline earlier this month after other networks supplying its connectivity to the Internet stopped carrying its traffic due to complaints it was complicit in cybercrime.
Since then the network has fought a cat-and-mouse game with network providers in 12 countries and international law enforcement, according to Jart Armin, the pseudonymous editor of the Hostexploit.com website, which has been involved in the action.
"Troyak is still fighting hard, as it is the only link to the outside Internet for a few [criminal groups]," he said in an email interview.
Troyak and another ISP, Group 3, provided connectivity for 90 of 249 servers used to control Zeus, a sophisticated piece of malware that steals financial credentials and other data. Group 3 has also been disconnected.
At this point, Troyak's reputation is so sullied that it is becoming difficult for it to find other ISPs to carry its traffic on the Internet.
That's an important point, because for Troyak to resume operations, it must find another company or organization that it can peer with in order to be reconnected to the Internet. Currently, even with Troyak offline, there are still 180 Zeus command-and control servers online, Armin said. Most of these are located in Russia and the Ukraine, however, making it easier for security researchers and law enforcement to stay on top of the problem.
"They're being pushed back into their own territory," Armin said.
On Sunday night, Troyak operators apparently hacked into servers in Latvia to get connectivity via an academic network in the country. But that effort was shut down with the help of Latvian law enforcement, Armin said.
On Monday, it appeared Troyak had peered with two upstream providers, wrote Mary Landesman, senior security researcher at ScanSafe, which is owned by Cisco Systems.
But that action appeared to be temporary, and as of Wednesday, Troyak was dead.
"Troyak seems to be down," said an administrator for Zeus Tracker. "And I believe that it won't come up again. Every ISP knows that Troyak is bad and won't peer/route their badness."
But there are signs its operators are making efforts to be reconnected. Computer security experts such as Joze Nazario of Arbor Networks are watching real-time routing tables, which show how Internet traffic is exchanged between ISPs and networks.
An entity called SAINTVPN is now carrying some of the traffic that used to be on Troyak, Nazario said.
SAINTVPN, which lists its location as St. Petersburg, Russia, was set up after the take-down effort and immediately started serving Zeus command-and-control commands, Armin said.
Security experts suspect that Troyak's operators have set up shop under a new name in order to secure a peering agreement with another network that is unaware of the name change.
In theory, it is possible that Troyak's servers could be available through SAINTVPN, but "we don't know if they are shuttered. We don't know if they are trying to find new upstream," Nazario said.
When networks agree to carry each other's traffic, they typically create some business agreement. But it's unknown what sort of business arrangement Troyak may have with SAINTVPN, Nazario said.
"It's an incredibly fluid situation," he said.
According to Armin, the other networks that are still actively hosting core Zeus command-and-control servers are:
AS # Name
24826 KHARKOV-TERMINALS-AS PE
29106 VOLGAHOST-AS PE
49314 NEVAL PE
47781 ANSUA-AS PE
47821 BOGONET-AS PE
"If we get all these, then Zeus will be toothless," Armin said.