Citadel, the aggressive botnet at the heart of a widely criticised takedown by Microsoft back in June, is back and stealing banking credentials from Japanese users, according to Trend Micro.
The security vendor claimed to have found “at least 9 IP addresses”, mostly located in Europe and the US, functioning as the botnet’s command and control servers.
Some 96 per cent of connections to these C&C servers come from Japan, proving that most of the banking Trojan infections are from that country alone, it said.
Trend Micro added the following in a blog post:
During a six-day period, we detected no less than 20,000 unique IP addresses connecting to these servers, with only a very minimal decrease from beginning to end. This means that there is still a large number of infected systems still stealing online banking credentials and sending them to the cybercriminals responsible.
The banks and financial institutions targeted in this campaign have already released warnings and advisories to their customers and loyalists regarding the attack itself. Users are reminded to read these warnings properly before logging into their online banking accounts.
As well as Japanese financial and banking organisations, the botnet has been targeting popular webmail services such as Gmail, Hotmail and Yahoo Mail, Trend Micro said.
Citadel was the subject of Operation b54, what Microsoft described back in June as its "most aggressive botnet operation to date". Working with the FBI, financial institutions and other technology firms, Redmond said it disrupted some 1,400 botnets associated with the Trojan, which had nabbed more than $500m from bank accounts around the world.
However, the initiative was slammed by the security community after Microsoft allegedly seized hundreds of domains as part of its swoop which were already being sinkholed by researchers to find out more about the botnet.
What’s more, UK security vendor Sophos claimed at the time that the takedown wasn’t nearly as successful as was initially made out.
Threat researcher James Wyke said in a blog post that only half of the 72 Citadel C&C servers Sophos was tracking appeared on Microsoft’s list.
Even worse, one in five of those on Redmond’s list failed to point to a sinkhole, implying “either that the sinkholing was unsuccessful or that the domains have already been re-appropriated by the Citadel botnet owners”, he added.
“Takedown efforts such as this can provide immediate benefit to the public by effectively disabling the control channels used to administer a very dangerous piece of malware,” said Wyke.
“However, the long-term effect of this particular takedown on Citadel is unlikely to be significant: it looks as though many of the botnets weren't knocked out, and rebuilding those that were taken down will not take long.”
It appears that those concerns were well founded. ®