In its statement to users, Twitter said that it reset the pilfered passwords which had been hacked and sent users emails advising them that they will have to create a new one.
Twitter noted a recent surge in security breaches at several U.S. media and technology companies.
The New York Times and The Wall Street Journal reported this week that their computer systems had been infiltrated by China-based hackers.
Twitter says hackers may have gained access to information on around 250,000 of its more than 200 million active users.
More top news
The pensioner, who is in her 70s, says her daughter has suffered from Huntington's disease.
US singer John Legend said he was "moved" by footage of the teenager singing one of his songs.
John Noakes was Blue Peter's longest-serving presenter.