Two pieces of malware software known as GOZeuS and CryptoLocker are at the centre of the alert.
People are being warned to make sure their security software is installed and up to date, and to run scans to check for any problems.
Important files should also be backed up, said the
"GOZeuS (also known as P2PZeuS) has been assessed as being responsible for the fraudulent transfer of hundreds of millions of pounds globally," said the NCA
"Recent intelligence has suggested that more than 15,500 computers in the
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