BestBuy.com, a leading retailer of electronics equipment, experienced Web site downtime from 11:19 p.m. Thursday, Dec. 14, until 8:30 a.m. the following morning, according to an Internet retailer monitoring service, WebSitePulse.com. Visitors attempting to use the site were shown a message asking them to come back later.

BestBuy.com spokesman Jay Mousolf said the BestBuy.com site was down for an hour around 11 p.m. Central Dec. 14 and went down again "for several hours" around 4 a.m. Dec. 15, for a total of about four hours of outage. No cause for the downtime was available.

WebSitePulse CEO Iavor Marinoff said the downtime could have been the result of a scheduled update or other maintenance to the site, although he added it was unlikely a planned maintenance event would have lasted for the nine-hour time span. BestBuy's Web site response times have been climbing as holiday shopping has become more active in December. The monitoring service had recorded an average response time of nearly 12 seconds for each user interaction on the BestBuy site. BestBuy is headquartered in Minneapolis, Minn.

"Our monitoring agent in Los Angeles first detected the malfunction at 11:19 p.m. EST and triggered the alarm," said Marinoff in a prepared statement. "BestBuy.com functionality was immediately tested from multiple locations in our network, as well as by an authorized technician, as part of our false alarm prevention procedure."

WebSitePulse regularly published reports on the response times of leading online retailers, including Circuit City, K Mart, Wal-Mart, Toys r Us, CompUSA, RadioShack, and Target. Wal-Mart experienced site outage on Black Friday, the first shopping day after Thanksgiving.

Editor's Note: This story was altered on Dec. 18 to add a response from BestBuy.