Clarksons said initial investigations show that the "unauthorised access was gained via a single and isolated user account, which has now been disabled.?
Police and lawyers were standing by to take what steps were available to prevent the spread of confidential information.
"Issues of cyber security are at the forefront of many business agendas in today's digital and commercial landscape and, despite our extensive efforts we have suffered this criminal attack," said Clarksons CEO Andi Case.
"We hope that, in time, we can share the lessons learned with our clients to help stop them from becoming victims themselves," he said.
Mr Case then appealed to clients to understand that "we would not be held to ransom by criminals, and I would like to sincerely apologise for any concern this incident may have raised.?
Earlier this year, Maersk Line and FedEx subsidiary TNT Express suffered a cyber attack, which has led to a wider discussion of cyber security measures in place in the industry.
Police and lawyers were standing by to take what steps were available to prevent the spread of confidential information.
"Issues of cyber security are at the forefront of many business agendas in today's digital and commercial landscape and, despite our extensive efforts we have suffered this criminal attack," said Clarksons CEO Andi Case.
"We hope that, in time, we can share the lessons learned with our clients to help stop them from becoming victims themselves," he said.
Mr Case then appealed to clients to understand that "we would not be held to ransom by criminals, and I would like to sincerely apologise for any concern this incident may have raised.?
Earlier this year, Maersk Line and FedEx subsidiary TNT Express suffered a cyber attack, which has led to a wider discussion of cyber security measures in place in the industry.