According a report Saturday in The New York Times, a group of cybercriminals used malicious software to steal at least $300 million from banks and other financial institutions around the world.

Kaspersky found that the hackers hit more than 100 institutions in 30 countries, dating back to 2013. The thefts could add up to $300 million and maybe more as Kaspersky thinks the attacks are ongoing.

Chris Doggett, managing director of the Kaspersky Lab North America market, told the Times: "This is likely the most sophisticated attack the world has seen to date in terms of the tactics and methods that cybercriminals have used to remain covert."

These attacks were carried out with the simple scam of sending infected emails to employees. Once they had access, the hackers set out to find employees who were in charge of cash transfer systems or ATMs. Next they installed a remote access tool, or RAT, enabling them to take screenshots or video of those employees' screens and study what they did, the Times said. It was then a simple task to use the info to transfer ATM monies to fake accounts.

Most of the banks that were hit are in Russia, but also on the list are ones in Japan, Europe and the United States.