Facebook has resolved a glitch that exposed passwords of millions of users stored in readable format within its internal systems to its employees.
The passwords were accessible to as many as 20,000 Facebook employees and dated back as early as 2012, cyber security blog KrebsOnSecurity, which first reported said in its report.
"These passwords were never visible to anyone outside of Facebook and we have found no evidence to date that anyone internally abused or improperly accessed them," wrote Pedro Canahuati, vice president of engineering, security and privacy at Facebook, via a company blog.
KrebsOnSecurity, citing a senior Facebook employee, said the an internal investigation by the company so far indicates that between 200 million and 600 million Facebook users may have had their account passwords stored in plain text.
Facebook said the issue was discovered in January as part of a routine security review. Majority of the affected were users of Facebook Lite, a version of the social media app largely used by people in regions with lower connectivity.
“This caught our attention because our login systems are designed to mask passwords using techniques that make them unreadable,” Canahuati said.
“We have fixed these issues and as a precaution we will be notifying everyone whose passwords we have found were stored in this way.”
The social network is also probing the causes of a series of security failures, in which employees built applications that logged unencrypted password data for Facebook users, the report said.
"We estimate that we will notify hundreds of millions of Facebook Lite users, tens of millions of other Facebook users, and tens of thousands of Instagram users," Canahuati added.
"In the course of our review, we have been looking at the ways we store certain other categories of information - like access tokens - and have fixed problems as we’ve discovered them.
"There is nothing more important to us than protecting people’s information, and we will continue making improvements as part of our ongoing security efforts at Facebook."
(Reporting by Shariq Khan and Munsif Vengattil in Bengaluru; Editing by Arun Koyyur)