Criminals have stolen millions of dollars from ATMs worldwide using a specialized malware program that forces the machines to dispense cash on command.The malicious program, dubbed Backdoor.MSIL.Tyupkin, is designed to work on ATMs running 32-bit versions of Windows from a major manufacturer, Kaspersky Lab researchers said Tuesday.Rather than remotely exploiting software vulnerabilities, the attackers infected the ATMs by gaining physical access to controls that are typically protected by a locked panel.The malware is installed by inserting a bootable CD into the machine, after which "the criminals reboot the system, and the infected ATM is under their control," Vicente Diaz, principal security researcher at Kaspersky Lab said via email. "This operation allows the criminals to play with the ATM software in the way that they need to. So it's a completely different threat level, where software protection doesn't work."Kaspersky Lab declined to name the targeted vendor, citing an ongoing investigation by Interpol into the compromises.Malware was found on 50 ATMs operated by banking institutions in Eastern Europe, researcher said. However, samples of the malware have been uploaded to VirusTotal from other countries, including the U.S., India and China, suggesting its use in those parts of the world as well.In the incidents investigated by Kaspersky Lab, the cybercriminals took several precautions to make their attacks harder to detect. For example, the malware was configured to only accept commands through the PIN pad during Sunday and Monday nights.In order to pull up the malware program's graphical interface on the screen, which displays how many bills are left in the ATM's cassettes and their denominations, attackers have to input a different session key every time. This key is generated based on an algorithm known only to the attackers, which prevents third parties from controlling the malware. Tyupkin's interface allows the operator to force the ATM to dispense 40 bills at a time from one of its cassettes.This malware-based attack is a natural evolution over credit-card skimming, which involves the installation of fake card readers and pin pads on ATMs to capture credit-card details, the Kaspersky researchers said. The Tyupkin malware is an example of attackers moving up the chain and targeting financial institutions directly, they said.Other security researchers have warned about the possibility of such attacks for years. In one of the most memorable presentations ever at the Black Hat security conference, a hardware hacker named Barnaby Jack compromised an ATM on stage in 2010, forcing it to spew out cash. Jack used a combination of physical access to the ATM's USB ports and a software exploit.Banks should review the physical security of their ATMs, replace all locks and master keys on the upper hood of the ATM machines and not rely on default locks provided by the manufacturer, the Kaspersky researchers said.Banks should also install alarm systems for physical access to the ATMs, they said: "The cyber-criminals behind Tyupkin only infected ATMs that had no security alarm installed."