LONDON — British officials issued an unusually stark alert about a cyberscam that locks users out of their computers unless they pay a ransom, saying Friday that tens of millions of people may soon be targeted.
In a warning headlined “URGENT ALERT,” Britain’s National Crime Agency said they were aware of a “mass e-mail spamming event that is ongoing” and urged computer users to beware of messages purporting to come from their bank.
Tony Neate, the chief executive of British Internet safety group GetSafeOnline, said it was noteworthy that the agency — often described as Britain’s equivalent of the FBI — had sent out such a strongly worded alert about a cyberscam.
The scam targeting Britons works by tricking people into downloading CryptoLocker, a new brand of malicious software that encrypts a user’s hard drive, effectively putting their photos, documents and other data under lock and key.



