Black hat hackers have created a new strain of Trojan that rewrites online bank statements to disguise fraud.
Victims of the URLZone Trojan would only realise their bank account has been looted after they check their balance with a bank branch or via an ATM.
The malware features a keystroke logger that captures bank login credentials and takes screenshots of activities on bank accounts, each of which were forwarded to a command and control server hosted in the Ukraine.
The Trojan agent gets instructions of how much to take from compromised online banking accounts and where to transfer funds from this server. Stolen funds are transferred to the bank accounts of money mules, who take a percentage of the money before sending the rest abroad using wire transfers.
The twist in what is thus far a fairly standard banking Trojan scam, comes in the tactics used by fraudsters to avoid detection, reports net security firm Finjan.
Once the money is stolen, the Trojan creates a forged bank statement to hide the theft. Furthermore the mechanisms of the scam are designed to stay "under the radar" of common anti-fraud systems at banks, Finjan explains.
To minimize detection by anti-fraud systems, the cybergang use various parameters to define the amount of money it will steal on each transaction. Criteria used by this cybergang included: making sure that the victim's balance is positive, ensuring that the amount to be stolen is not too high, setting a random amount on each transaction and making sure that the remaining balance remains positive.
A gang of cybercrooks was able to steal €300,000 ($438,000) from German bank accounts over 22 days using the tactic, Finjan reports. The Israeli-based security firm has turned over its file on the scam to the German authorities.
"To avoid detection, cybercriminals continue to improve their methodologies for stealing money and going under the radar from the victims and banks alike," said Yuval Ben-Itzhak, CTO of Finjan. "With the combination of using sophisticated Trojans for the theft and money mules to transfer stolen money to their accounts, they minimize their chances of being detected."
Finjan's latest cybercrime report explains the attack in more depth and goes on to explain how consumers and banks might go about protecting themselves against the new threat.
Other security researchers are taking the threat seriously. Anti-spyware firm Sunbelt, for example, describes the evolution of a Trojan that can display fake bank balances as the "next big [ugly] thing" in banking fraud malware. ®