Troubled telecoms giant TalkTalk saw more than a tenth of its value wiped off in trading today, with MPs now set to launch an inquiry into the recent cyber attack.
Shares plummeted more than 12% today, adding to the 4.3% drop suffered on Friday as the firm struggles to manage the fallout from last week's hack, which saw potentially huge amounts of customer data stolen.
There will now be an inquiry into the hack, launched by Jesse Norman, chair of the Culture, Media and Sport Select Committee.
In an earlier development, the chief executive of TalkTalk warned of a "cyber security arms race" threatening all UK companies as she revealed she called in defence experts over the hack of its website.
Dido Harding said she contacted BAE Systems, which supplies cyber security to government agencies.
She also warned any company in the UK could be vulnerable and said she still was unsure how many customers had been affected.
Police are investigating last week's attack, which TalkTalk said had affected its website rather than its "core systems".
Baroness Harding told the Times: "This is a sort of cyber security arms race. Criminals are learning how to do things. One of the first calls I made on Wednesday was to BAE."
The company has claimed data stolen in the attack would not allow criminals to plunder customers' bank accounts, as complete credit card details were not stored in its system and account passwords were not accessed.
The peer also told the Daily Telegraph: "Do I wish I had done more? Of course I do. But would that have made a difference? If I'm honest I don't know.
"This is happening to a huge number of organisations all the time. The awful truth is that every company, every organisation in the UK needs to spend more money and put more focus on cyber security - it's the crime of our era."
Scotland Yard is investigating alongside the National Crime Agency (NCA), but no arrests have been made.
Officers are investigating a ransom demand sent to the telecoms giant following the attack by someone claiming to be responsible and seeking payment. The firm said it was not sure if the message was genuine.
The latest breach is the third in a spate of cyber attacks affecting TalkTalk in the last eight months, with breaches in August and February also resulting in customers' data being stolen.