Following the incident, Angling Direct has appointed external cybersecurity specialists to investigate the cause of the interference.
An Angling Direct spokesman said: "Work continues around the clock to bring the websites back online while our 39 retail stores across the UK have remained open and continue to trade.
"As a precaution, the company has notified the relevant regulators and law enforcement agencies, including the Information Commissioner's office in the UK.
"We are mindful of our obligations regarding data. It is too soon yet to make any determination around the impact this incident has had on personal data, but we will inform any individuals in line with our regulatory obligations should there be a need to do so.
"Importantly, the company does not hold any customer financial data as our website transactions are handled by third parties.
"As matters currently stand, the board does not anticipate that this incident will have a detrimental impact on underlying trading and the company will continue to assess any cost exposure that this incident may create.
"The board will provide a further update as and when appropriate and apologises for any disruption that has been caused to customers by this incident."