TalkTalk said it lost 95,000 customers following the cyber attack it suffered in October as it revealed its latest financial results.
The UK operator was the target of a “significant and sustained” hack that affected 157,000 of its customers.
In total, TalkTalk said it lost 101,000 subscribers in the three months to December as the company admitted that it had taken “longer than expected” to return the business to normal operational effectiveness.
The time when it was offline affected its ability to upsell its services, notably mobile, which in part led to churn of 2.1 percent.
TalkTalk said exceptional costs of restoring its online capability with enhanced security features, associated IT, incident response and consultancy costs, as well as the free upgrades it offered, are expected to total £40-45 million.
It put the trading impact of the quarter’s events on its balance sheet at £15 million.
Revenues rose 1.8 percent with sales related to customers connected directly to TalkTalk's own network up 4.5 percent.
The company said it expected to deliver “a material step up in profits” before the end of the next quarter as it reported lower than forecast earnings.
Last week, police in India arrested three people working for Wipro, TalkTalk's call centre provider, for breaching policies and contract terms.
CEO Dido Harding (pictured) said: “It is encouraging to see the business returning to normal after a challenging quarter that was dominated by the cyber attack.
“Our customers have responded well, with almost half a million customers choosing to take up our unconditional offer of a free upgrade.
“Both churn and new connections recovered during December and January and independent external research has revealed that customers believe that we acted in their best interest.
“As the value for money telecoms provider we are well placed to benefit from the current regulatory reviews in the sector and expect to see quad play driving sustainable long-term growth.”