By Jonathan Davies
WHSmith has blamed a "bug" customers' personal information inadvertently being sent to magazine subscribers.
The retailer said details like names, addresses and contact information were sent to other customers via email.
WHSmith stressed that no payment or credit card details had been leaked.
In a statement, WHSmith said: "We have been alerted to a systems processing bug by I-subscribe, who manage our magazine subscriptions. It is a bug not a data breach.
"We believe that this has impacted fewer than 40 customers who left a message on the 'contact us' page where this bug was identified, that has resulted in some customers receiving emails that have been misdirected in error."
"We can confirm that this issue has not impacted or compromised any customer passwords or payment details," said WHSmith.