Utility firm Southern Water has admitted that nearly half a million customers may have been affected by a data breach.

In a blog post, it said that personal details for 5% to 10% of its 4.6 million customers had been stolen by hackers.

According to a report by the BBC, the data included names, dates of birth, national insurance numbers and bank account details. While it didn’t specify which details were accessed, the firm said it would be contacting customers affected by the breach.

“We are very sorry that this has happened,” Southern Water said in the post. “We continue to work with our expert technical advisers to confirm whose data is at risk. Our initial assessment is that this is the case for some of our customers and current and former employees.”

The leak was first detected after the firm noticed suspicious activity on its IT systems in January. It then employed independent cyber-security experts to monitor the dark web and try to find the information that had been stolen.

However...