Instagram exposed user credentials in plain text. THe number of users is not yet disclosed, but the company says it affected "a very small number of people." 

In late August, Instagram had another security flaw allowing hackers to gain access to phone numbers and emails for many "high profile" users. Also reported that month, hundreds of instagram users were locked out of their accounts caused by a widespread hacking campaign. 

These social sites are rich with personal identifiable information from millions of daily active users and will continue to be targeted by hackers.