Ad spending on Twitter dropped by a staggering 71 percent in December, according to data from an advertising research company. The figures from Standard Media Index highlight the scale of the challenge before new Twitter CEO Elon Musk in convincing former advertisers to come back to the site after many reduced their spending or stopped altogether over concerns about his stewardship. A separate analysis from research firm Pathmatics showed that most of the companies shut down their ad spending in November—the month when Musk restored many suspended accounts and set up a new paid verification system that hoaxsters hijacked to pose as legitimate corporations.