The malware, called ‘Android.Bankosy,’ has been updated to intercept the codes, which are part of so-called two-factor authentication systems.
Many online banking applications require a login and password plus a time-sensitive code in order to gain access. The one-time passcode is sent over SMS but also can be delivered via an automated phone call.
Some banks have moved to call-based delivery of passcodes. In theory, that provides better security since SMS messages can be intercepted by some malware, discussed Dinesh Venkatesan of Symantec in a blog post recently.
But, Bankosy has been updated to forward all calls to the attackers, Venkatesan said. “In the Asia-Pacific region, many operators use a service code in the format *21*[destination number]# to forward calls, which Bankosy has implemented.
“The malware also has support for disabling and enabling silent mode in addition to locking the device so that the victim is not alerted during an incoming call,” Venkatesan explained.
The one-time passcode is used with the victim’s login credentials, which the attackers have presumably already obtained.
Symantec detected Bankosy in July 2014. A technical write-up from that time shows the malware also prompted victims to enter their payment card information in a more bold attempt at fraud.