The UK's National Cyber Crime Unit has issued a warning that a mass spamming operation is taking place, targeting tens of millions of UK email addresses.

Cryptolocker Ransomware Campaign
A screenshot of the type of message which will appear if your PC is infected with Cryptolocker malware.

The National Crime Agency has issued the warning of a mass "email spamming event" in which online account holders receive emails that appear to be from banks and other financial institutions.

Although the email may be sent to tens of millions of UK customers the campaign appears to be targeting small and medium businesses in particular. The NCA has not said yet if the people affected have had their details hacked from some company's database, though it appears likely if such a large volume of emails is being sent out.

The emails contain an attachment which appears to be correspondence linked to the person's account. It is in fact a piece of malware known as Cryptolocker, which, if installed on your PC, will lock you computer, encryt all information on the hard drive (such as documents, videos and photos) and demand payment through bitcoin in order to decrypt the information.

Encrypted

If the victim doesn't pay up in time, then the cyber-criminals behind the campaign will erase the encryption key it holds and the information will be effectively lost forever.

Once encrypted, the computer will display a splash screen with a countdown timer and a demand for the payment of two bitcoins in ransom. Two bitcoins is currently worth approximately £536.

Earlier this week F-Secure seaurity researcher Sean Sullivan warned IBTimes UK that Cryptolocker was likely to be used more and more by cyber-criminals, becasue of the anonymity afforded by using bitcoins for payment.

Sullivan added that the criminals behind the ransomware typically released the information if the victim paid up, but warned they also deleted teh encryption key once the countdown timer expired.

Lee Miles, Deputy Head of the NCCU says "The NCA are actively pursuing organised crime groups committing this type of crime. We are working in cooperation with industry and international partners to identify and bring to justice those responsible and reduce the risk to the public."

The NCA is currently investigating the matter but as of yet doesn't know the source of the email addresses or where the cyber-criminals are based.