US-Twitter has warned that hackers acting on behalf of governments may have accessed the phone numbers of some users.

A security researcher discovered a flaw in its contacts upload feature in December that allowed him to access the phone numbers of senior politicians.

Around that time, Twitter said it saw a “high volume of requests” to use the feature from Iran, Israel and Malaysia.

It declined to say how many users’ phone numbers had been exposed.

In a statement published on its blog Twitter said: “ It is possible that some of these IP addresses may have ties to state-sponsored actors. We are disclosing this out of an abundance of caution and as a matter of principle.”

It did not provide much detail on why it thought it could have been a state-based attack but one clue may lie in the fact that users in Iran appeared to have had access to the platform, even though Twitter is banned in the country.

Phone numbers

In December, TechCrunch reported that security researcher Ibrahim Balic had managed to match 17 million phone numbers to specific Twitter users accounts by exploiting a flaw in the contacts feature in Twitter’s Android app.