A quarter of a million Twitter users have had their accounts hacked after the social networking site revealed its security had been breached by large-scale cyber attacks.
Twitter noted a recent surge in security breaches this week at several U.S. media and technology companies.
The New York Times and The Wall Street Journal reported that their computer systems had been infiltrated by China-based hackers.
Twitter issued a message to reassure its users after the social networking site detected "unusual access patterns" that led to "unauthorized access attempts to Twitter user data".
It said that is has reset the pilfered passwords which had been hacked and sent users emails advising them that they will have to create a new one.
Privately held Twitter, which has 200 million active monthly users, said it was working with government and federal law enforcement officials to track down the attackers.
Twitter, the social network known for its 140-character messages, could not speculate on the origin of the attacks as its investigation was ongoing, said spokesman Jim Prosser.