Nineteen people arrested after computer hackers swiped up to £6m from online bank accounts in Britain are being quizzed by police.
Zeus is a "trojan" virus that hides on machines, bypassing security software
Millions of pounds were taken in just three months by a hi-tech gang.
They used a virus known as "zeus" to infect computers and capture the passwords and other sensitive details of banking customers.
Their money was then transferred into bogus accounts created by the crooks to help them launder it.
It is not yet known which banks are affected.
Detective Chief Inspector Terry Wilson, of the Metropolitan Police, said the amount of money stolen is likely to "increase considerably" as the investigation continues.
He said: "We believe we have disrupted a highly organised criminal network, which has used sophisticated methods to siphon large amounts of cash from many innocent people's accounts.
The officer said banks have had to repay the stolen money "at considerable cost to the economy".
"Online banking customers must make sure their security systems are up to date and be alert to any unusual or additional security features requested which is at variance with their normal log-on experience," DCI Wilson continued.
"Greater public awareness and education will make it harder for personal details to be compromised and for this type of fraud to be carried out."
Officers from the Met's Central E-Crime Unit arrested 15 men and four women aged between 23 and 47 at addresses across London in dawn raids on Tuesday.
They were questioned on suspicion of fraud, offences under the Computer Misuse Act and money laundering.
Experts believe thousands of computers have been infected with malicious computer codes, including zeus.
It is a "trojan" virus that hides on machines, bypassing security software before capturing and transmitting log-on information, passwords and other data.
Last year, £59.7m was lost to online banking fraud, according to Financial Fraud Action UK. Another £440m was lost to credit card fraud.
Zeus is a "trojan" virus that hides on machines, bypassing security software
Millions of pounds were taken in just three months by a hi-tech gang.
They used a virus known as "zeus" to infect computers and capture the passwords and other sensitive details of banking customers.
Their money was then transferred into bogus accounts created by the crooks to help them launder it.
It is not yet known which banks are affected.
Detective Chief Inspector Terry Wilson, of the Metropolitan Police, said the amount of money stolen is likely to "increase considerably" as the investigation continues.
He said: "We believe we have disrupted a highly organised criminal network, which has used sophisticated methods to siphon large amounts of cash from many innocent people's accounts.
The officer said banks have had to repay the stolen money "at considerable cost to the economy".
"Online banking customers must make sure their security systems are up to date and be alert to any unusual or additional security features requested which is at variance with their normal log-on experience," DCI Wilson continued.
"Greater public awareness and education will make it harder for personal details to be compromised and for this type of fraud to be carried out."
Officers from the Met's Central E-Crime Unit arrested 15 men and four women aged between 23 and 47 at addresses across London in dawn raids on Tuesday.
They were questioned on suspicion of fraud, offences under the Computer Misuse Act and money laundering.
Experts believe thousands of computers have been infected with malicious computer codes, including zeus.
It is a "trojan" virus that hides on machines, bypassing security software before capturing and transmitting log-on information, passwords and other data.
Last year, £59.7m was lost to online banking fraud, according to Financial Fraud Action UK. Another £440m was lost to credit card fraud.
