Facebook users' personal information could have been accidentally leaked to third parties, in particular advertisers, over the past few years, according to Symantec's official web blog.
Third-parties would have had access to personal information such as profiles, photographs and chat, and could have had the ability to post messages, Symantec's web blog said.
"We estimate that as of April 2011, close to 100,000 applications were enabling this leakage," the blog post said.
" ... Over the years, hundreds of thousands of applications may have inadvertently leaked millions of access tokens to third parties," posing a security threat, the blog said.
The third-parties may not have realised their ability to access the information, the blog post said.
Facebook was notified of this issue and has confirmed the leakage, the post said.
The blog also said Facebook, the world's largest social networking website, has taken steps to resolve the issue.
Facebook was not immediately available for comment.
Facebook has more than 500 million users and is challenging Google and Yahoo for users' time online and for advertising dollars.
(Reporting by Thyagaraju Adinarayan, editing by Bernard Orr)