Access to hundreds of thousands of Facebook accounts may have accidentally been leaked because of a flaw in some applications.

Security firm Symantec discovered that programs were inadvertently sharing access tokens which could be used by advertisers.

It estimates that, as of last month, 100,000 applications were still enabling leaks.

Facebook said that it was improving authentication methods.

"We have been working with Symantec to identity issues in our authentication flow to ensure that they are more secure," Facebook's Naitik Shah wrote in a blog post on Tuesday.

Full story: BBC News