Online retailers that use WorldPay's internet payment system, which has been subjected to a denial-of-service attack since Tuesday, may be in line for compensation.
Owned by the Royal Bank of Scotland, WorldPay is still no closer to stopping the digital assault which is hammering online retailers worldwide.
The attack has affected the company's payment and administration networks.
The situation has improved slightly, as the website is back up and email has been restored, but the system is still clogged and many customers are still unable to gain access.
WorldPay came under fire from small businesses last month for its long settlement periods. The latest news will not help relations with its customers.
"We're not in a situation where we've solved the problem. The system is transacting in low volumes," said a spokesman.
"There has been an orchestrated, malicious, third-party effort which has blocked the pipe that links us to the outside world."
He added that, although "some shoppers using WorldPay powered sites can transact in the usual way, the service will be unavailable to some".
Over the issue of compensation to online retailers that have lost business, the spokesman stated: "We are willing to enter into dialogue with retailers on a case by case judgement, but our priority now is getting the service restored."
The company stressed that "the integrity and security of our systems and data is in no way compromised. It is purely a matter of the network capacity being overloaded by the deliberate actions of a third party."
Commons Science and Technology Committee calls for new post-Brexit skilled-workers immigration system
Committee calls for visa-free travel and permit-free work for skilled workers
Eleven 'normal' outer moons, and one described as 'oddball' found circling Jupiter
Scientific discovery has found a quadrillion tonnes of diamonds in the earth's mantle
Mobile payment app makes users' details public by default