Twitter's real-time search function stopped working at around 3.30am on Monday morning, and was out of action for three hours.
The function is increasingly used by businesses to manage brands, track how influencers think and feel, and respond to customer comments.
Twitter's new Trending Topics feature, which relies on the search function, stalled for the same period of time, much to the frustration of the site's users.
"Twitter is busted right now. Search was dead for hours, plus there is the unfollow problem and others," said a user called KW2P.
Even though real-time search results have started coming through again, many tweets could be lost for ever.
"There's a four-hour gaping hole of no tweets in Twitter Search. Fail," remarked Twitter user ItsNeet.
"Where are they? Outerspace?" added a user called JFSX.
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