-- Twitter sent a warning to some users that the social network said may have been targeted by "state-sponsored hackers."
It's unclear how many people received a letter from Twitter. However, the message warns hackers may be attempting to steal phone numbers, along with email and IP addresses, according to copies of the email shared on Twitter. It was also unknown who the reported hackers are and who they could be working for.
"At this time, we have no evidence they obtained your account information, but we're actively investigating this matter," a copy of the letter posted online by @Coldhak, a Canadian nonprofit group, said. "We wish we had more we could share, but we don't have any additional information we can provide at this time."
Among the people who reported receiving the letter were security researchers, activists and journalists.
Twitter did not immediately respond to ABC News' request for comment.