XM Satellite Radio restored service to its subscribers Tuesday after a software glitch knocked out the signal from one of its four satellites, the company said.

It's not clear how many of the company's eight million subscribers were hit by the outage, but customers in both Canada and the United States appear to have been affected, according to Jason Mercier, a media spokesman for Canadian Satellite Radio/XM Radio Canada.

The disruption — which caused some customers to lose service and others to experience "significantly degraded service" — occurred about noon on Monday, the company said. It returned on Tuesday at 12:45 pm ET.

"The problem occurred during the loading of software to a critical component of the satellite broadcast system, which resulted in a temporary loss of signal from one of the company's satellites," the company said on its website.

The company apologized to consumers in a brief statement Tuesday, and advised users to wait five to ten minutes after turning on the radio to reacquire the XM signal.

No other statement has been released in either the U.S. or Canada.

XM Radio Canada has about 237,500 subscribers, according to their most recent figures from February 28, 2007. Subscribers pay $14.99 a month in Canada for the service.

XM launched four satellites between 2001 and 2006. The first two have experienced problems and are now regarded as "in-orbit" spares, according to the company's annual report.

In February, Washington-based XM and Sirius Satellite Radio Holdings Inc. proposed a $13-billion US merger deal that must meet approval of the Federal Communications Commission in the United States.

If approved, the merger would give the combined company a monopoly in the business of beaming programs to people who buy special radios.

With files from the Associated Press