TalkTalk said it lost over 100,000 customers and suffered costs of £60m as a result of a cyber-attack on the company in October, the Guardian reports.
Financial results from the telecoms firm revealed a trading hit to the tune of £15m, alongside exceptional costs of £40m-£45m, taking the total bill for the attack to £60m.
The figures act as warning to other firms to ensure they have they have their IT systems sufficiently protected – TalkTalk chief executive, Dido Harding, has since admitted that in hindsight the company should have done more to protect itself.
Security experts also accused the firm of a disregard for the safety of its customers' data, suggesting that it shouldn't have taken the police intervention for TalkTalk to own up to the problem.
Despite only 4% of the company's four million customers having been affected by the attack and no financial loss incurred by customers despite the partial disclosure of payment details, TalkTalk customers initially appeared to lose some faith in the provider.
However, although TalkTalk gained fewer customers than expected following the attack because it closed down online sales operations, half a million existing customers took up the option of a free upgrade.
That offer of compensation has helped improve the trust in the TalkTalk brand since the attack, Harding says, citing independent external research.
She added: "It is encouraging to see the business returning to normal after a challenging quarter that was dominated by the cyber-attack. Both churn and new connections recovered during December and January and independent external research have revealed that customers believe that we acted in their best interests."