The large-scale outage in BlackBerry service on Tuesday and Wednesday was caused by an unessential upgrade, Research in Motion at last confirmed today. A newly optimized routine that RIM said hadn't been properly optimized had been installed on its servers, triggering a crash that even the failsafe systems for the network were unable to catch.

Though the company said it was still studying the circumstances that led to the shutdown, it has ruled out hardware failures and security breaches as the cause and said that there was nothing inherent to its software design that could repeat the crash. An official statement has yet to be released.