Financial services provider Liberty announced on Saturday evening that it has been hacked.
In a notice on its website the company said it has been "subjected to unauthorised access to its IT infrastructure".
"An external party claims to have seized data from us, has alerted us to potential vulnerabilities in our systems and has requested compensation for this," states the notice.
Liberty said that, since becoming aware of the hack, it has taken "immediate steps" to secure its computer systems.
"Liberty is investigating the breach and we will endeavour to keep all stakeholders fully informed as appropriate," it stated.
"We are working hard to rectify the situation."
The Sunday Times reported that the hackers want "millions" from Liberty or they will start releasing "sensitive" information about "top clients".
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