Virgin Media said it recently became aware that one of its marketing databases was incorrectly configured which allowed unauthorised access.

The telecoms giant said it immediately shut down access to the database which contained some contact details of around 900,000 people.

However, it stressed that the database did not include any passwords or financial details, such as credit card or bank account numbers.

But personal details such as names, home and email addresses, as well as phone numbers were exposed.

Virgin Media’s investigation suggests the database was accessed on at least one occasion but at this stage, it doesn’t know the extent of the access or if any information was actually used.

Lutz Schüler, CEO of Virgin Media, said: “We are now contacting those affected to inform them of what happened. We urge people to remain cautious before clicking on an unknown link or giving any details to an unverified or unknown party. Online security advice and help on a range of topics is available on our website.

“Protecting our customers’ data is a top priority and we sincerely apologise.

“We have kept the Information Commissioner’s Office fully updated since we became aware of this incident.”

‘Customers likely to be worried’

Adam French, Which? consumer rights expert, said: “This data breach has exposed the data of almost a million Virgin Media customers and whilst no financial details or passwords were included, those customers are likely to be worried. It is vital that Virgin Media continues to provide clear information on what has happened.

“For anyone concerned they could be affected – it’s good practice to update your password after a data breach. Also, be wary of emails regarding the breach, as scammers may try and take advantage of it.”

Virgin Media is the third big brand to be impacted by a data breach this week, following Boots’ move to suspend millions of Advantage Card payments and Tesco blocking 600,000 Clubcard accounts as a result of security issues.