“We’re taking this step because of vulnerabilities that need to be addressed by mobile carriers and our reliance on having a linked phone number for two-factor authentication (we’re working on improving this),” Twitter said.

It added, “We’ll reactivate this in markets that depend on SMS for reliable communication soon while we work on our longer-term strategy for this feature.”

The decision comes after a hacker group called Chuckling Squad hijacked the account of Twitter CEO Jack Dorsey and posted offensive messages and even bomb threats. The unauthorized tweets were visible for roughly half an hour before being removed.