Most can be recognised quite easily, as they have a very simple subject line, containing the words 'Overdue invoice' followed by what looks like an 11-digit invoice reference; however, the invoice does not really exist.
There is also typically an email attachment in the .arj format, which is a method of compressing a file or folder into a single, smaller archive, and may have the risk of including files infected with a computer virus.
A look at the originating IP addresses of the mail servers used to send these emails reveals that they are coming from all over continental Europe, from Germany to Romania, which suggests that this is a broadly targeted spam attack.
Some of these mail servers are already on the blacklists of certain internet service providers, but with a large number of server locations being used, it is unlikely that your email spam filters will catch all of the emails.
What can I do?
The most obvious thing you can do is to be very wary of any emails you receive relating to overdue invoices, especially if you can't remember the transaction they refer to, or the original email address is located outside of the UK.
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Don't open email attachments unless you are sure of what they are - and even if they come from an address you recognise, it's often best to double check with the person you think has sent the email, before you click on any files.
Of course, if you keep on top of your invoices, you should be able to feel more confident that you are up to date with any payments, so any claim of an overdue invoice is easier to ignore.
Knock-on credit control problems
Finally, a word of warning for small businesses - with this spam issue in circulation, you could encounter knock-on effects for your own credit control.
Any emails you send out to your own customers reminding them about overdue invoices risk being mistaken for spam and simply ignored or deleted.
This makes it more important than ever to ensure attempts at debt recovery are sent regularly and from a legitimate source - including writing through the post if emails are unsuccessful.
Of course, taking a pragmatic approach to your invoicing to encourage customers to pay in full and on time is still the best solution.
In this way, you can make sure that as few invoices go overdue as possible - making it unnecessary to chase them, and avoiding the risk of your communications being dismissed as spam by the recipient.