Twitter turns off Tweet via SMS feature for an unspecified period following abuses that led to hackers posting from at least two high-profile accounts. One of the victims was Jack Dorsey whose feed got hijacked on Friday and posted racial slurs and even a fake bomb threat at the Twitter headquarters. Twitter concluded that the hack occurred because of a security oversight from the mobile carrier, which allowed an unauthorized party to tweet using the text messaging service. Both hacks were possible due to vulnerabilities affecting the ability to tweet via SMS. Twitter plans to improve the feature and reactivate it in markets that depend on SMS for reliable communication.
Source: https://www.bleepingcomputer.com/news/security/twitter-suspends-sms-based-tweeting-after-high-profile-account-hacks/