The system failure caused panic among BNY Mellon's US fund management clients over concerns that hundreds of funds may have been traded at inaccurate prices during a week of especially high market volatility.

"SunGard deeply regrets the that this issue has impacted BNY Mellon and its clients," read the statement. "While we are confident that no data was lost as a result of the incident, calculation and processing of net asset values (NAVs) of certain mutual funds and ETFs was disrupted."

According to investment research firm Morningstar, as of Wednesday as many as 796 funds were without NAVs.

SunGard also stated that the outage was not caused by "any external or unauthorised systems access", nor was it a result of "recent turmoil in the equity markets". Instead the problem was an unforeseen complication resulting from an operating system change carried out by SunGard last Saturday.

While the same procedure had previously been carried out successfully at other firms and had also been completed under test conditions, in applying the change to BNY Mellon's production environment, it became corrupted. Furthermore the back-up facility hosted by SunGard concurrently corrupted preventing an automatic failover.

SunGard says it is confident that this was "an isolated incident due to the physical/logical system environment and not an application issue with InvestOne itself".

It is now workng with BNY Mellon to restore the aforementioned production environment and to work through the backlog caused by the outage.

"We take this issue very seriously and truly appreciate the spirit of cooperation from BNY Mellon," added SunGard president and CEO Ross Fradin.