The company hasn't provided a detailed explanation for what happened, but Jack Dorsey's account fell victim to a "security oversight" at his carrier that let people send tweets via text through his phone number. It's not clear if this is the result of SIM hijacking, a spoofing attempt or something similar.

Whatever the cause, it's a drastic step. SMS-based tweeting has been a core element of Twitter since the very beginning, and it's been available long since the majority of people switched to posting from apps and websites. Not that Twitter necessarily had much choice. Attackers are eager to exploit this lapse in security, and there's no quick fix -- this at least buys the company some time.