A data-stealing Trojan called Ice IX allows cyber criminals to divert customers' calls to their banks in the UK and US.
Ice IX, a variant of the ZeuS financial malware platform, captures bank account information. But it can also capture information on the telephone accounts of online banking customers, according to researchers at security firm Trusteer.
“This allows attackers to divert calls from the bank intended for their customer to attacker-controlled phone numbers,” said Amit Klein, chief technology officer at Trusteer.
Cyber criminals are executing fraudulent transactions using the stolen credentials and redirecting the bank’s post-transaction verification phone calls to professional criminal caller services that approve the transactions, he said.
In one attack captured by Trusteer researchers, at login the malware stole the victim’s user ID and password, memorable information/secret question answer, date of birth and account balance.
Next, the victim was asked to update contact phone numbers and select the name of their service provider from a drop-down list, including BT, TalkTalk and Sky
To enable the attacker to modify the victim’s phone service settings, the victim is then asked to submit their telephone account number.
“This is very private data, typically only known to the phone subscriber and the phone company, and is typically used by the phone company to verify the identity of the subscriber and authorise sensitive account modifications such as call forwarding,” said Klein.
The fraudsters justify this request by saying the information is required as a part of verification process caused by "a malfunction of the bank’s anti-fraud system with its landline phone service provider".
“Fraudsters are increasingly turning to these post-transaction attack methods to hide fraudulent activity from the victim and block e-mail and phone communication from the bank,” said Klein.
This allows attackers to circumvent security mechanisms that look for anomalies once transactions have already been executed by the user, Klein said.
However, Klein said post-transaction attacks like these can be detected by security systems that search for specific malware characteristics before transactions are submitted and allow the online banking application to stop fraud by changing business flows such as blocking money transfers and declining to add a payee.