Twitter has sent emails to an unknown number of users warning them that their accounts may have been “targeted by state-sponsored actors.” The alert is the first of its kind to come from the microblogging site.

The emails explained that hackers may be trying to obtain information such as phone numbers, email addresses and IP addresses, according to Twitter users who received the alerts. The messages went on to say that although Twitter has no evidence that those responsible had managed to obtain the information, it has reason to believe the recipients were the intended targets.

A Canada-based nonprofit organization, Coldhak, posted a copy of the letter it received on Twitter: “At this time, we have no evidence they obtained your account information, but we’re actively investigating this matter… We wish we had more we could share, but we don’t have any additional information we can provide at this time.”

The notice also said that Twitter believed the number of targeted accounts “to be small,” and added that it might be of “particular concern if you choose to Tweet using a pseudonym” – something that millions of Twitter users do.

The emails recommend users to take appropriate precautions to protect their personal information and even include a link to anonymous communications software Tor.

Twitter isn’t making any official comment on the matter or denying that the emails were sent. Some of those targeted apparently included journalists and security researchers, a few who are engaged in activism and connected to the Tor Project in some capacity, according to Motherboard.

There has been no indication given of which state may be behind the attacks, but whenever the term “state-sponsored” gets mentioned, suspicion tends to be directed at the usual suspects of China, North Korea, and Russia. But there’s always the chance that the US could be behind the attempted breach.

Google also sends out warnings to users if it suspects state-sponsored attackers may be trying to compromise their accounts or computers, and it was reported in October that Facebook had started to notify people it believes have accounts that are being spied on by government agencies such as the NSA.