The identities of “tens of thousands” of British people are up for sale on the Dark Web.
The details of more than 600,000 customers were reportedly stolen from companies in the UK last year.
The average cost for a Briton’s personal details is $30 (£20), a Whitehall security official said.
Profiles have been stolen from the UK government’s own computer systems that hold enough detail to take control of a person’s digital identity.
A government spokesman said: “We are looking carefully at the level of regulation. Every company board should be fully aware of the risk from cyber attack and be confident that the company has proper security in place.”
The dark web, described as the internet black market, cannot be accessed with the usual search engines such as Google, instead requiring the use of a covert internet browser called TOR.
A report by antivirus and web security experts Symantec released in April said there were almost one million new cyber threats released online every day last year, with five out of six large companies globally targeted.
Phone and broadband provider TalkTalk was targeted a week ago. It said bank account numbers and sort codes, like those printed on a cheque, may have been accessed.
The company has said criminals would need more information to enable them to take money from a customer’s account, adding: “Even then, the chances are very small indeed.”
TalkTalk chief executive Dido Harding said she was still unsure how many of the telecoms giant’s four million UK customers had been affected by the attack, which hit its website rather than its “core systems”. As part of a joint operation between the Met’s cyber crime unit, the PSNI’s cyber crime centre and the National Crime Agency, officers are investigating a ransom demand sent to the firm by someone claiming to be responsible and seeking payment.
A 15-year-old boy arrested in County Antrim, Northern Ireland as part of the investigation has been released on bail until a date next month.