Confessing to a cyber-attack used to be an eerily quiet business. Shares could shrug and sales remain steady when confidential customer data or vital intellectual property were lost, as confused consumers and investors did not know how to react.

But when Target admitted last week that the data of more than 70m customers were stolen in a Thanksgiving cyber-attack, something unusual happened: it damaged its business. The US retailer warned that sales would decline this quarter because the theft had scared off customers. It has since acknowledged that patrons who shopped at the retailer outside the November 27 to December 15 period may have also been affected.

Cyber-attacks are on the rise with cyber-security experts warning that retailers in particular have become vulnerable.