Facebook has banned a third-party quiz app amid concerns over the possible misuse of users' data and pulled its own security software from Apple's app store after the iPhone maker tightened data security rules.

The social media company said Wednesday it took action against the myPersonality app because its creators refused an inspection, and over worries that data on as many as 4 million users may have been misused.

Facebook is particularly vexed about anything relating to the misuse of data following the Cambridge Analytica scandal earlier this year. Allegations that political consultancy used personal information harvested from 87 million Facebook accounts have seriously dented the company's reputation as well as its stock market value. Facebook has investigated thousands of apps and suspended more than 400 apps over data sharing concerns.

Facebook said it moved to ban the myPersonality app after it found user information was shared with researchers and companies "with only limited protections in place."

The company said it would notify the app's users that their data may have been misused. It's only the second time Facebook has banned an app, after it blocked one linked to Cambridge Analytica.

It said myPersonality was "mainly active" prior to 2012, and it wasn't clear why Facebook was taking action now.

The app was created in 2007 by researcher David Stillwell and allowed users to take a personality questionnaire and get feedback on the results.

"There was no misuse of personal data," Stillwell said in a statement, adding that "this ban appears to be purely cosmetic." Stillwell said users gave their consent and the app's data was fully anonymized before it was used for academic research. He also rejected Facebook's assertion that he refused to submit to an audit, saying the company knows he is willing to provide information.

Separately, Facebook also removed its Onavo Protect virtual private network app from Apple's store after the iPhone maker brought in tighter data security rules for applications. Onavo Protect could no longer be found on Apple's store on Thursday but was still available on the Google Play store for Android phones.

Facebook acquired Onavo, an Israeli company, in 2013. Its VPN software is aimed at helping users secure their personal information over public Wifi networks and alerting them when apps use too much data. But the company also said that it may collect users' mobile data traffic and that aroused concerns about privacy.

"We've always been clear when people download Onavo about the information that is collected and how it is used," Facebook said in a statement. "As a developer on Apple's platform we follow the rules they've put in place," referring to Apple's revised app store guidelines released in June.

Among the changes is a new section on data security requiring developers to "implement appropriate security measures to ensure proper handling of user information."