Twitter on Wednesday shut off the ability to send tweets via text message, a feature that dates to the service’s earliest days but was used last week to hack CEO Jack Dorsey’s account.

The step is temporary but necessary to protect accounts, the company said in a series of tweets.

“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),” the company said

Two-factor authentication is a means of adding another layer of security to online services, requiring people to receive a temporary code via text message in order to complete a login.

On Friday, Dorsey’s account was hacked by one or more people who sent more than a dozen racist and otherwise offensive tweets over the course of 20 minutes. Twitter said that a phone number associated with his account was compromised due to a “security oversight by a mobile provider,” allowing someone to compose and send tweets via text message.

It wasn’t immediately clear how many of Twitter’s users would be affected by the change. Many of Twitter’s 139 million daily users tweet via its phone app or through a browser, although sending tweets via text message can be useful for people without the app.

Twitter said it would reactivate the feature “in markets that depend on SMS for reliable communication soon while we work on our longer-term strategy for this feature.”

Earlier on Wednesday, the Twitter account of actress Chloë Moretz appeared to have been compromised by the same group of hackers that accessed Dorsey's account.