U.S. social media network Facebook Inc. said late Wednesday that about 4 million of its users may have their private data misused by a third-party app on its platform.

  Facebook acknowledged the data abuse risk in an official blog post, saying it has banned quiz app myPersonality, which was active mainly until 2012.

The app has been blocked for "failing to agree to our request to audit and because it's clear that they shared information with researchers as well as companies with only limited protections in place," the post said.

The company said it has notified the 4 million people who chose to share their Facebook information with myPersonality. However, it found no evidence that myPersonality accessed the information of those users' friends.

Since March this year Facebook has investigated thousands of apps in a campaign to crack down on third-party apps that illegally share user data.

More than 400 apps have been suspended across its platform since then, it said.

Facebook has been going through a hard time since earlier this year, when its CEO Mark Zuckerberg was summoned to testify before Congress in Washington after reports that British political consultancy Cambridge Analytica "improperly" gained access to information about at least 87 million of its users.

U.S. federal regulators have been pressing the company to take measures to better protect user privacy.