Authorities from the UK National Crime Agency have issued an unusual alert on Friday about a rampant cyberscam that locks users out of their computers and demands a pricey ransom in return. Tens of millions of Brits have been targeted.

In a warning titled with “ALERT”, the NCA's National Cyber Crime Unit announced that a "mass email spamming event" was occurring and encouraged computer users to be wary of emails coming from their banks or financial institutions.

It seems a round of ransomware is going around, disguised as bank notices, and it's primarily headed toward small and medium-sized businesses. The emails, described as a "significant risk," are loaded with a Trojan attachment called Cryptolocker. It's a malicious software that encrypts hard drives, essentially locking a user's photos, documents, etc.

The Cryptolocker will quietly install and encrypt documents. When it's done wreaking havoc, a 72-hour countdown clock will appear and demand ransom or else it will not decrypt a user's files...permanently. The ransom is set at 2 Bitcoins. That's about £536 or $800.

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Some who have paid the ransom have reported that their files are decrypted within a few hours, according to The Washington Post. The NCA however does not endorse paying the ransom and even said "there is no guarantee" that the malware would decrypt files once receiving payment.

An investigation into the source of the emails is ongoing. The NCA recommended that anyone infected with the malware report their case via Action Fraud.