The experts at Kaspersky Lab have discovered evidence of a targeted attack against the clients of a large European bank. According to the logs found in the server used by the attackers, apparently in the space of just one week cybercriminals stole more than half a million euros from accounts in the bank.

The first signs of this campaign were discovered on 20 January this year when a C&C server was detected on the net. The server’s control panel indicated evidence of a Trojan program used to steal money from clients’ bank accounts.

The experts also detected transaction logs on the server, containing information about which sums of money were taken from which accounts. All in all, more than 190 victims could be identified, most of them located in Italy and Turkey. The sums stolen from each bank account, according to the logs, ranged between 1,700 to 39,000 euros.

The campaign was at least one week old when the C&C was discovered, having started no later than Jan. 13 2014. In that time the cybercriminals successfully stole more than 500,000 Euros. Two days after GReAT discovered the C&C server, the criminals removed every shred of evidence that might be used to trace them. However, experts think this was probably linked to changes in the technical infrastructure used in the malicious campaign rather spelling the end of the Luuuk campaign.

“Soon after we detected this C&C server, we contacted the bank’s security service and the law enforcement agencies, and submitted all our evidence to them,” said Vicente Diaz, Principal Security Researcher at Kaspersky Lab.

Malicious tools used

In the LUUUK case, experts have grounds to believe that important financial data was intercepted automatically and fraudulent transactions were carried out as soon as the victim logged onto their online bank accounts.

“On the C&C server we detected there was no information as to which specific malware program was used in this campaign. However, many existing Zeus variations (Citadel, SpyEye, IceIX, etc.) – have that necessary capability. We believe the malware used in this campaign could be a Zeus flavor using sophisticated web injects on the victims,” added Vicente Diaz.

Money divestment schemes

The stolen money was passed on to the crooks’ accounts in an interesting and unusual way. Our experts noticed a distinctive quirk in the organization of the so-called “drops’ (or money-mules), where participants in the scam receive some of the stolen money in specially created bank accounts and cash out via ATMs.

There were evidences of several different “drop’ groups, each assigned with different sums of money. One group was responsible for transferring sums of 40-50,000 Euros, another with 15-20,000 and the third with no more than 2,000 Euros.

“These differences in the amount of money entrusted to different drops may be indicative of varying levels of trust for each “drop’ type. We know that members of these schemes often cheat their partners in crime and abscond with the money they were supposed to cash. The Luuuk’s bosses may be trying to hedge against these losses by setting up different groups with different levels of trust: the more money a “drop’ is asked to handle, the more he is trusted,” added Vicente Diaz.

The C&C server related to The Luuuk was shut down shortly after the investigation started. However, the complexity level of the MITB operation suggests that the attackers will continue to look for new victims of this campaign. Kaspersky Lab’s experts are engaged in an on-going investigation in The Luuuk’s activities.