Clarksons has been targeted by cyber criminals and is on standby with police to take action against any stolen data that may be released.
London-listed Clarksons says the hit came via a single account but stresses the incident has not impacted its ability to do business.
Chief executive Andi Case said: "Issues of cybersecurity 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.
