Such unsolicited email scams are not rare – previous variants have targeted users of online payment service PayPal. They rely on a reasonable proportion of the millions of people who receive the email being Citibank customers, and on a proportion of these customers falling for the trick.

The Citibank scam is likely to have fooled fewer people than some similar efforts, as it was riddled with grammatical mistakes. One paragraph read, We are letting you know, that you, as a Citibank checking account holder, must become acquainted with our new Terms & Conditions and agree to it.