TheWorks.co.uk PLC (LSE:WRKS) said its trading and business is disrupted and some stores closed because of a cyber attack.
Though there was no compromise of payment data, the company said the full extent of the attack is not known and it has informed the Information Commissioner's Office.
The on-line retailer has suspended deliveries to stores and extended the deadline for fulfilling online orders.
However, online and store deliveries will resume shortly, the company said.
Since it became aware of the incident, it disabled all external and internal access to its systems, including email, while advisors are helping to resolve the issue.
A team of forensic cyber security experts has been appointed and investigations are underway at the firm.
It stressed the incident will not adversely affect company forecasts or financial position.
TheWorks said customers can continue to shop safely in store and online since debit and credit card information is processed securely outside of the group's systems, through accredited third parties.