Microsoft has apologised for a brief outage which saw its search site Bing disappear from the internet.
The outage lasted for nearly 30 minutes in the early hours of 3 December. At that time anyone visiting the site got an error message.
A Microsoft statement said the outage was caused by a "configuration change" made to the site during testing.
This, it said, had "unfortunate and unintended consequences" which included making the site unavailable.
Writing on the Bing blog Satya Nadella, one of Microsoft's senior vice presidents in its Online Services Division, said the mistake led to people either being unable to find the site or having their queries returned unanswered.
"As soon as the issue was detected, the change was rolled back, which caused the site to return to normal behavior," wrote Mr Nadella.
Detecting the problem and fixing it took about 30 minutes, he said.
Mr Nadella added that Microsoft was looking into the genesis of the incident to find out what needs to be done to stop such an incident happening again.
Microsoft has worked hard to position Bing as a serious rival to Google and the unscheduled downtime will dent this image. As soon as the mistake became apparent messages about it on microblogging site Twitter started to appear.
In response Tony Chor, a Bing engineer, Tweeted that Microsoft was working on bringing the site back up.
Not all aspects of the Bing service were knocked out by the configuration change. Many reported that Bing Maps was still available.
This week Microsoft updated Bing Maps to add test features that allows applications, such as real time traffic feeds, to be added to the site. It also introduced a system that lets people create 360 degree panoramas of locations.
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