Twitter was down for many users on Thursday and the hot micro-blogging service said it was trying to fix the problem.
Many Twitter users stopped receiving the 140-character-or-less messages known as "tweets" shortly before 11:00 am (1500 GMT).
The service was still disrupted more than three hours later.
"We are currently investigating a problem causing many users' timelines to be delayed," Twitter said in a brief message at Twitter.com.
In another update a short time later, it said "timelines remain stale for users. We are deploying fixes to address the problem."
Twitter last month closed a deal for "significant" new financing despite having yet to show how it is going to make money.
The San Francisco-based company did not reveal the amount of the funding but The Wall Street Journal and The New York Times put the figure at up to 100 million dollars and said it valued Twitter at one billion dollars.
Twitter has grown rapidly in popularity since it was launched in August 2006 and claims to have topped 50 million users.
Twitter last suffered a major disruption in August when it came under a distributed denial of service (DDoS) attack along with Facebook and other social networking sites.
The accounts of a pro-Georgian blogger were identified as the target of the DDoS attacks believed to be an attempt to silence his online criticism of Moscow's role in last year's Georgia-Russia war.
Classic DDoS attacks involve legions of zombie computers, machines infected with viruses, which are commanded to simultaneously visit a website.
Such a massive onslaught of demand can overwhelm website computer servers, slowing service or knocking it offline entirely.Reuse content