Online payment service WorldPay is still struggling to maintain the availability of its systems in the face of a "sustained" denial of service attack.
WorldPay, which is part of the Royal Bank of Scotland Group, was initially hit on Tuesday by the massive DoS attack, which flooded the company with bogus requests and brought its payment and administration systems to a grinding halt.
Customers, including Vodafone, Sony and hundreds of online retailers, who use WorldPay to process card transactions, were notified of the problems in an email yesterday. WorldPay said it was filtering and re-routing requests and giving customers the option of accessing a back-up service.
Simon Fletcher, head of UK communications at WorldPay, told silicon.com the company was aiming to restore something like normal service today but he admitted that the continued attack is still affecting availability.
"Though many of the measures we put in place yesterday are working effectively, the 'denial of service' attack is being sustained and availability of our systems is at times intermittent as a result of this," he said.
Fletcher stressed that the integrity of WorldPay's systems had not been compromised and that the attack was purely aimed at knocking the service offline by overloading it with bogus requests.
"We are continuing to execute our contingency plans and are committed to achieving full restoration of the service as soon as we are able. We are keeping our customers briefed through all means possible," he said.