Microsoft Tuesday began delivering an update to Windows Phone 8 smartphones that provides unspecified "performance enhancements" that some customers say include an OS fix for random reboots and Wi-Fi enhancements.

A spokeswoman said Tuesday that "Microsoft isn't going into detail into the specific enhancements at this time."

Microsoft is working with carriers and hardware partners to get the update tested, approved and rolled out, she added. "Some customers are starting to receive it now," she said.

Customers on online forums late yesterday reported the delivery of an update called Portico for the Windows Phone 8 HTC 8X that provides fixes for random rebooting problems and adds a Wi-Fi enhancement.

Users last month began reporting random reboots on both HTC 8X and Nokia Lumia 920 smartphones supplied by various carriers around the globe.

Microsoft acknowledged the problem announced on Nov. 27 that a fix for the unexpected reboots was in the works and would be released sometime in December.