"We have become aware of an issue related to one of our support forms, which is used by account holders to contact Twitter about issues with their account," Twitter said in a press release. "This could be used to discover the country code of people's phone numbers if they had one associated with their Twitter account."
The issue did not expose the full phone numbers or any other personal information of any impacted accounts, the release said. Twitter has directly informed people who were identified as being affected by the issue, it added.
Twitter highlighted that during its investigation into the issue, the company noticed some unusual activity involving the affected customer support form Application Programming Interface, the release said. The company saw large numbers of inquiries coming from IP addresses located in China and Saudi Arabia, the release said.
Although Twitter cannot confirm the intent or attribution, it is possible that some of the IP addresses may have ties to state-sponsored actors, the release said. Law enforcement has been briefed on the findings, the release said.