London: Up to 100 banks and financial institutions worldwide have been attacked in an "unprecedented cyber robbery", a media report said Monday.
Russian computer security firm Kaspersky Lab estimates $1 billion has been stolen in the attacks, which it says started in 2013 and are still active, BBC reported.
A cyber criminal gang with members from Russia, Ukraine and China is responsible, it said.
Kaspersky said it worked with Interpol and Europol on the investigation.
It said the attacks took place in 30 countries, including Russia, the US, Germany, China, Ukraine and Canada.
"These attacks again underline the fact that criminals will exploit any vulnerability in any system," Sanjay Virmani, director of Interpol's digital crime centre, said.
Kaspersky said the gang's methods marked a new stage in cyber robbery where "malicious users steal money directly from banks and avoid targeting end users".
The gang, which Kaspersky dubbed "Carbanak", used computer viruses to infect company networks with malware including video surveillance, enabling it to see and record everything that happened on staff's screens.
In some cases it was then able to transfer money from the banks' accounts to their own, or even able to tell cash machines to dispense cash at a pre-determined time of day.
Kaspersky said on average each bank robbery took place between two and four months, with up to $10 million stolen each time.
"It was a very slick and professional cyber robbery," Kaspersky Lab's principal security researcher, Sergey Golovanov said.