Hang Seng Indexes, which manages the Hang Seng group of indices, said the technical glitch in its system which disrupted trading late last month was caused by an unusual sequence of events.
Updating of major indices for half an hour on January 22 was disrupted by the glitch and the group said it was carrying out a study to identify possible areas for improvement.
In a report to the Legislative Council's financial affairs panel, Hang Seng Indexes said the factors that caused the problem were so rare that it could not have been foreseen.
'We're talking about something that happened within a thousandth of a second, or even less,' Vincent Kwan Wing-shing, director of Hang Seng Indexes, said.
Kwan said the incident was the first major technical mishap that had occurred in the system, which remained 'highly resilient'.
The glitch meant that the Hang Seng Index and the Hang Seng China Enterprises Index could not be calculated properly from 10am to 10.32am, although individual share prices continued to function.
The company resorted to using a backup system and e-mailed index updates to vendors every 15 minutes.
Hang Seng Indexes said it has not received any complaints from people seeking compensation.
Kwan denied the problem had anything to do with the huge volume of trades that the system manages, or was caused by the sheer weight of indices that the company compiled.
He said it would not be necessary for the Hong Kong stock exchange to move towards a US-style model where there are multiple index companies in operation.
The company has set up a working group to look into improving its contingency system to shorten the time required to inform the market should another technical error arise.
'We cannot say that something like this won't happen again, but if it does we are confident we have the capacity to handle it,' Kwan said.