Twitter went offline for almost two hours on Thursday, in an outage that the social media platform -- used by hundreds of millions worldwide -- blamed on a technical glitch.
The company said there was no evidence that its security had been breached.
It marked a new setback for the company, which late Thursday altered its policies on hacked content after accusations of bias stemming from its decision to block a news report critical of Democratic White House candidate Joe Biden.
"We are continuing to monitor the issue, and things appear to have returned to normal," Twitter's application programming interface site said at 0011 GMT Friday.
The California-based company tweeted earlier: "We had some trouble with our internal systems and don't have any evidence of a security breach or hack."
According to downdetector.com, users on every continent had reported being unable to use the platform, but the outages were concentrated on the east and west coasts of the United States, as well as Japan.
The outage appeared to have started around 2130 GMT.
- Bias? -
The Twitter shutdown came at a delicate moment. The company this week took the dramatic step of reducing the reach of a New York Post article critical of Biden, because of the possibility that the story was based on hacked information.
The decision drew a harsh rebuke from conservatives.
On Thursday Twitter said that, under changes to its Hacked Materials Policy, it would "no longer remove hacked content unless it is directly shared by hackers or those acting in concert with them."
Thursday's outage was the latest technical breakdown to knock Twitter offline. The platform experienced an hour-long outage in July 2019, one lasting several hours a year ago and yet another last February.
More worrisome are hacking attacks on popular social media platforms like Twitter.
In July, prominent Americans including former president Barack Obama, Amazon founder Jeff Bezos, Microsoft founder Bill Gates and Tesla chief Elon Musk saw their Twitter accounts hacked.
The attack targeted at least 130 accounts, with tweets posted by the intruders duping people into sending $100,000 in Bitcoin, supposedly in exchange for double the amount sent.
Several people, aged 17 to 22, have since been charged for the hack, in which they targeted Twitter employees for personal passcodes to get into the company's internal systems.
In September 2019, Twitter experienced a brief but embarrassing attack: the account of its founder Jack Dorsey was hacked and erratic and offensive messages were posted from it.