British spook hive MI5 has taken the unusual step of placing a front-page warning on its website about a financial scam carried out by people pretending to be spies or the agency's director general.

The online alert was prominently posted on mi5.gov.uk, and occupies more space than the UK security threat level indicator, which describes the danger to Brits as "substantial".

The blurb reads:

Warning: Financial scams referring to MI5 and its Director General Members of the public in the UK and abroad have received requests for money by email or phone from individuals claiming they work for the Security Service (MI5). Some have purported to be from MI5's Director General, Sir Jonathan Evans. These requests are a financial scam and have nothing to do with the Service or the Director General. If you receive such a communication, please do not respond to it and report it to the police.

As David Harley, a senior researcher at security software firm Eset points out, the warning is not specific and therefore difficult to act upon.

"It might have been useful to know more about the type of scam the warning refers to," Harley noted in a blog post. "It could, after all, be anything from a 419 to some form of ransomware, and the ways of recognising and dealing with those different kinds of scam can be very different. But I have yet to find an actual example."

Of the two possibilities suggested by Harley, ransomware would appear more likely than bogus offers to shift seized assets and the like, the staple of advanced-fee fraud (aka 419 scams).

Ransomware locks up systems and accuses the user of some crime, from using illegal file-sharing networks to distributing child-abuse images. Strains of ransomware, such as Reveton, often sport police logos to make them look legit. Victims are tricked into coughing up a "fine" of about €100 using untraceable cash vouchers in order to obtain codes to unlock their computers. Samples of Reveton masquerading as a piece of FBI software have been widely found, as an alert by the US Internet Crime Complaint Center (IC3) illustrates.

Similar software nasties flashing MI5's logo and name around, instead of the Metropolitan Police or FBI badges, are all too easy to imagine. That said, MI5 specify contact by email or phone, which would seem to indicate other methods. It's also possible the security agency's warning actually refers to a round of 419 scams or even a hard-up rogue agent who really needs the cash. ®