BAE Systems has been hired to investigate the cyber-attack on TalkTalk’s computer systems that may have led to the theft of data on four million customers.
On Friday, the ISP admitted that its systems had been compromised and later revealed that an unidentified party had submitted a ransom demand for the attack.
A spokeswoman for BAE's Applied Intelligence division said the company's cyber-specialists were analysing vast quantities of data to help establish how the breach happened and what information was stolen.
"The financial information they have on its own is not enough for them to access your bank account,” said TalkTalk CEO Dido Harding.
"We now expect the amount of financial information that may have been accessed to be materially lower than initially believed and would on its own not enable a criminal to take money from your account."
Despite this, British newspapers on Sunday carried stories of individuals who said callers posing as TalkTalk employees had taken money from their bank accounts.
Many customers took to social media to complain about their treatment following the attack which is the ISP’s third data breach this year. Some had been told they faced hundreds of pounds in fees to leave the provider.
Data released by the Office for National Statistics this month showed there were nearly 2.5 million incidents of cyber-crime in the year to June 2015.
Britain's Information Commissioner watchdog, which can impose fines of up to £500,000, has said it is looking into the incident but security experts said the prevalence of cyber-crime showed more needed to be done.
Simon Moores, chair of the International eCrime Congress, criticised the commission for failing to take action.
"The Information Commissioner needs to have more powers to reflect the direction of travel...at a time of rampant identity theft and exploitation of financial details," he said.
"You need to encourage a culture and a level of responsibility where all large organisations...take serious ownership and responsibility for the privacy of people's financial and personal data rather than having a cavalier attitude, which we have seen in so many cases."
Moores believes that Britain should give responsibility for information security to a single minister rather than have it spread across several government departments.
Earlier this month, a hacker managed to steal the personal details of 15 million T-Mobile customers in the US.