Twitter said users whose security was compromised will be receiving an email with instructions to create a new password.
"Your old password will not work when you try to log in to Twitter," said Bob Lord, Twitter's director of security.
We encourage all users to take this opportunity to ensure that they are following good password hygiene, on Twitter and elsewhere on the Internet.
Make sure you use a strong password – at least 10 (but more is better) characters and a mixture of upper- and lowercase letters, numbers, and symbols
Twitter also advised that users do not use the same password more than once across other services and accounts.
More top news
Following Theresa May's announcement of her plans for Brexit, how have newspapers across Europe and the UK reacted?
At least four people have been killed after gunmen opened fire at government offices in the Mexican beach resort of Cancun.
The mobile phone provider was fined by Ofcom after overcharging around 40,000 customers nearly £250,000 over calling "150."