Sage Pay has apologised for a four hour outage yesterday that left online merchants with no way to process payments for Christmas orders.
Simon Black, managing director of Sage Pay, said: "I deeply regret the impact that we've had on your business, at what is the worst possible time for our systems to fail."
The length of the downtime was blamed on "systems diagnostics being carried out to pinpoint the root cause".
Sage Pay online payment processing was unavailable for most customers between 6pm and 10pm yesterday, Monday 6 December.
The company said the problem was caused by running a background job which caused "an existing, but unknown, hardware flaw".
Simon Black told the Reg: "We were running a data processing report which caused an overload which then led to a hardware failure. Because we were unable to diagnose quickly what had gone wrong we were unable to go straight to a back up system.
"But there was no loss of data and there is no backlog of orders."
Black said customer reaction was mixed - he emailed customers early this morning explaining the problem. He said some replies thanked him for the company's openess but others were understandably angry.
Black said: "I and my team deeply regret this downtime and apologise to our customers. It was an isolated incident and the same issue will not happen again."
Black said the issue is identified as fully resolved and "was not related to our new system infrastructure."
Go here to see the email from Sage Pay's Simon Black. ®