Brits have been urged to protect themselves from cyber attacks after criminal hackers stole £20 million from UK bank accounts.
The warning from the National Crime Agency (NCA) came after it emerged that thieves had used "particularly virulent" malware to siphon money from the accounts of innocent victims.
At least one "significant arrest" has already been made, and thousands of accounts are believed to have been affected by the use of the Dridex malware by sophisticated online criminals.
Consumers have been urged to make sure their operating systems and anti-virus software are up to date to prevent attacks.
Mike Hulett from the NCA said: "This is a particularly virulent form of malware and we have been working with our international law enforcement partners, as well as key partners from industry, to mitigate the damage it causes.
"Our investigation is ongoing and we expect further arrests to made," he added.
How does the scam work?
Criminals have developed the malicious Dridex software (malware) - also known as Bugat and Cridex - to target financial institutions and payment systems around the world.
Computers can become affected by the virus when users open documents in emails they believe to be legitimate.
The software can then harvest users' online banking details, allowing criminals to steal money from users' accounts.
According to the NCA, thousands of computers in the UK could have been infected, with the majority being Windows users.
What is being done to stop it?
The National Crime Agency says it and the United States' FBI are attempting to "sinkhole" the malware by stopping the infected computers - known as a "botnet" - from communitating with the criminals who are attempting to control them.
It says a large portion of the botnet has been rendered "harmless" and are now helping the victims.