Today I got a third one of those scam emails and so I had a look on the Web to see how common it is. It has been around in the US for a few months and seems to have started there with letters first. It's now happening here by email and is being referred to under the title `My nickname in darknet is'. An example of one of the web discussions from recent days is here:
LINK One of the people posting on there has been checking the bitcoin account named in the email and says money is flowing into it, so some folk are paying up even though it's a scam. Presumably they have a guilty conscience. It's comforting to see others receiving the scam messages and confirming that it is a scam and that the perpetrators are not really getting access to computers.
Later...I followed advice on the Action Fraud web site and sent a text file with the message source of the three email messages to the City of London Police National Fraud Information Bureau.