The cyber attack on TalkTalk could cost it up to £35 million the company has said.

TalkTalk hack to cost up to £35 millionFollowing the hack- which divulged some users’ financial details, all customers of the telecoms group will be offered a free upgrade.

Chief executive Dido Harding said that despite the hack, TalkTalk was “well positioned to deliver strong and sustainable long-term growth”.

The firm expects still full year results to be in line with market expectations.

TalkTalk shares had jumped more than 13% by the close of trade on Thursday- but were still down more than 20% compared with their pre-hack value.

Speaking to the BBC, Ms Harding said: “The estimated one-off costs are between £30 million and £35 million – that’s covering the response to the incident, the incremental calls into our call centres, obviously the additional IT and technology costs, and then the fact that over the last three weeks until yesterday our online sales sites have been down, so there will be lost revenue as a result.”

She added that in recognition of the uncertainty that this had caused customers, they would be offered an upgrade.

A spokesperson said the type of upgrade offered would depend on the kind of package customers already had. For example, customers with TV packages might be offered a sports channel that they did not already have.

Customers who were financially affected directly will be free to leave TalkTalk without financial penalty. They would have to be able to show they had lost money as a result of the hack.

Customers who wish to leave for a different reason – for example, if they feel their data is not secure – would still have to pay a contract termination fee.

However Talk Talk’s offer to it’s customers is very limited

Some of TalkTalk’s millions of customers might have been angry enough to try to terminate their contracts when the telecommunications company first revealed details of a major data security breach last month.

But, with contracts for mobile, fixed line, broadband and television services of up to two years (always worth looking at those few lines at the bottom of the paperwork) customers found they couldn’t leave TalkTalk without incurring hefty costs.

When Dido Harding, the chief executive, first announced that customers would only be able to leave if they could show a “direct impact” on their bank account – a pretty high bar – investors heaved a sigh of relief and TalkTalk’s share price bounced up.

More than 15,600 bank account numbers and sort codes were stolen. Four people have been arrested and bailed in connection with the hack.

Ms Harding told the BBC that it was “too early to tell” what the longer term impact of the breach would be on the business.