An MIT study tracked 126,000 stories and found that false ones were 70 percent more likely to be retweeted than ones that were true. Matt Rourke/AP hide caption

One of the new, longer tweets. Twitter hide caption

The Twitter symbol appears above a trading post on the floor of the New York Stock Exchange. Richard Drew/AP hide caption

Milo Yiannopoulos, a conservative writer and Internet personality, holds a news conference down the street from the Pulse nightclub in Orlando, Fla., last month. Drew Angerer/Getty Images hide caption

Twitter's board named co-founder Jack Dorsey the company's permanent CEO last week. Justin Tallis/AFP/Getty Images hide caption

A worker unveils a floor mat bearing the logo of Twitter on the floor of the New York Stock Exchange. Andrew Burton/Getty Images hide caption