A piece of malicious software called Tyupkin has allowed criminals to dispense millions of dollars in cash from ATMs in Eastern Europe and elsewhere, prompting an INTERPOL investigation.

Kaspersky Labs was among the first to announce the alert about this malware, also known as Backdoor.MSIL.Tyupkin. Unlike other forms of cybercrime affecting the financial services industry, this ATM security breach involves direct physical contact with the machines, where criminals insert a bootable CD containing the Tyupkin malware. Working most likely at night on Sundays and Mondays, the criminals reboot the ATMs and enter a combination of digits on the keypad, which can result in the bank machines spitting out 40 bills at a time.

A story on ZDNet noted that while the attacks involved manual intervention, hard disk encryption and BIOS passwords could have been used to thwart the attackers. On the other hand, the Tyupkin malware works in such a way that the keypad sequence to dispense the cash is unique to each session. In other words, the algorithm makes it much harder for others to control the malware.

This is by no means the first time security experts have thought through the potential risks regarding ATMs. An analysis on PCWorld recalled a demonstration of how ATMs could be compromised at the Black Hat security conference four years ago, using a combination of USB ports and a software exploit. Tyupkin, however, is an escalation of how cybercriminals are operating compared to more commonplace approaches, such as installing fake card readers and PIN pads in ATMs, otherwise known as credit card skimming.

The International Business Times said Europe, Latin America and Asia have all found ATMs infected with Tyupkin. The malware affects machines running 32-bit versions of Microsoft Windows, but while INTERPOL investigates, the name of the ATM vendor has not been released, nor has the estimated number of individuals involved in the thefts.

Threatpost added that at least four samples of Tyupkin have been uploaded to VirusTotal from the United States and China and that the latest version of the malware (version .d) includes anti-debug and anti-emulation features. It also disables application security software from “a particular vendor,” which was not named.

Reports from several sites suggested that banks might be best protected by ensuring all the locks and master keys on the top of ATMs are replaced and secured properly.