THE NCA's National Cyber Crime Unit are aware of a mass email spamming event that is ongoing, where people are receiving emails that appear to be from banks and other financial institutions.
The email has an attachment that looks legitimate but is malware that encrypts computer files.
If the attachment is opened, a displayed countdown timer demands a ransom to decrypt the files.
The malware installs a piece of "ransomware" called Cryptolocker on computers running the Windows operating system.
The ransom demands that the user pay two Bitcoins, a virtual currency, that would be worth £536 to release the decryption key.
Reports suggest that people who have paid the ransom have not had their files decrypted and it has been impossible to restore encrypted files.
When using your home computer for internet access be warned not to click on any suspicious attachments, to have updated antivirus software and to regularly back up files.
More advice can be found at the government's web site GetSafeOnline