It said myPersonality shared user information with researchers and companies with “only limited protections in place.”
“As a result we will notify the roughly four million people who chose to share their Facebook information with myPersonality that it may have been misused,” Facebook’s vice president of product partnerships Ime Archibong said.
The app was created by researcher David Stillwell and allowed users to take a personality questionnaire and get feedback on the results.
In a statement to Fortune magazine, Mr Stillwell disputed Facebook’s claims, saying “all necessary consents were explicitly and repeatedly provided by all Facebook users when using the myPersonality app”.
He added: “When the app was suspended three months ago I asked Facebook to explain which of their terms was broken but so far they have been unable to cite any instances.”
Facebook also revealed that it has so far suspended more than 400 apps over data sharing concerns since launching an investigation in March.
The social media giant has been under intense scrutiny since revelations that political consultancy Cambridge Analytica had improperly used people’s personal information in the run-up to the US presidential election and Brexit vote.
“Since launching our investigation in March, we have investigated thousands of apps,” Mr Archibong said.
“And we have suspended more than 400 due to concerns around the developers who built them or how the information people chose to share with the app may have been used – which we are now investigating in much greater depth.
“It’s also why we’ve changed many of our policies – such as our expansion of App Review and our new policy that no information will be shared with apps if you haven’t used them in 90 days.”