Twitter under FTC investigation for alleged misuse of user data - CNET | The Marteq Alert | Scoop.it
The investigation apparently relates to a revelation Twitter made last year in which it informed users that had recently discovered that users' email addresses and phone numbers meant to be used for security reasons "may have inadvertently been used for advertising purposes." 

That information is supposed to be used solely for account protection purposes, but Twitter said advertisers were able to tap the phone numbers to target commercials, through the company's "Tailored Audiences" and "Partner Audiences advertising system.