Twitter’s secret revenue weapon is your data that they sell

In its IPO filing Thursday, Twitter Inc. disclosed how much the microblogging platform earned from a lesser-known side business: $47.5 million came from selling off its data to a fast-growing group of companies that analyze the data for insights into news events and trends.

That is a small amount compared with the revenue generated from advertising, but Twitter’s data business has rippled across the economy. The site’s constant stream of experiences, opinions and sentiments has spawned a vast commercial ecosystem, serving up putative insights to product developers, Hollywood studios, major retailers and—potentially most profitably—hedge funds and other investors. Backed by millions of dollars in venture capital, hundreds of “social listening” firms have emerged.