Four people have been arrested following the suspected theft of £1m from two UK banks using computer malware.
Police also seized £80,000 in cash and a live hand grenade following raids in the Enfield and Islington areas of north London.
The arrests follow complaints by a number of bank customers that they accidently downloaded complex malware on to their computers after opening emails purportedly from their bank.
Scotland Yard said that a total of £1m was siphoned from the banks in this way and transfered into different accounts waiting to be laundered and withdrawn. The banks have not been named.
Two 31-year-old men, a 27-year-old woman and a 24-year-old woman were arrested on suspicion of conspiracy to defraud, conspiracy to launder money, and possession of an explosive.
Det Chief Insp Jason Tunn, of the Met's Cyber Crime Unit, said: "These arrests follow an investigation into what we suspect is an international and organised crime, targeting a number of bank customers in London and across the UK.
"The victims have been hoodwinked by malware-carrying emails purporting to be from their banks, and subsequently had money taken from their accounts.
"The Met's Cyber Crime Unit is determined to protect people and businesses in London from cyber crime, which can see businesses ruined and people's hard-earned money taken from them in a second. We are working closely with the banking industry to achieve that.
"We will also seek to restrain and seize criminal profits where possible, in order to remove the financial benefit of online crime from cyber criminals."
The male suspects are currently in custody at a central London police station. The women have been bailed until next year.