Search engine Bing's outage in China last week was a technical error, rather than an intentional censorship block, a source familiar with the matter said, although Chinese authorities and Microsoft have not commented on the topic.
From a technical perspective, a person at Microsoft told Reuters, the site appeared to have been blocked in a manner similar to sites blocked by the government.
But the company had received no prior notice from authorities, and the disruption was not intentional on the part of the government, added the person, who declined to be identified, citing the sensitivity of the matter.
Microsoft was not immediately available for comment on Monday. Last week, although it confirmed the outage, it declined to give details.
The Cyberspace Administration of China did not respond immediately to a faxed request from Reuters seeking comment.
Starting from Thursday, Internet users in China attempting to access cn.bing.com, the search engine's domestic URL, found themselves directed to an error page.
Service had resumed by late on Friday, however.
Engineers at ExpressVPN, a provider of virtual private network (VPN) software allowing internet users in China to access censored websites, ran tests during the outage to determine its origin.
They found that rather than domain name service (DNS) poisoning, the most common means for blocking sites under the Great Firewall, Bing's outage appeared to employ a technique known as "black-holing".
With this method, rather than re-directing to a dummy server traffic headed for a specific website, the traffic is simply cut off en route, usually at the internet service provider (ISP) level.