Facebook's retroactive purge of data collection abusers is underway.

In a blog post, Facebook delivered an "update" on its efforts to audit all apps that had access to large amounts of data, prior to the policy change it made in 2014 banning the mass collection technique used by Aleksandr Kogan and Cambridge Analytica.

To date, Facebook says is has investigated "thousands" of apps. It has already suspended around 200 apps, pending further investigation into whether their data collection constituted misuse.

"The investigation process is in full swing," Ime Archibong, Facebook's VP of product partnerships wrote. "We have large teams of internal and external experts working hard to investigate these apps as quickly as possible."

The investigation is making good on Mark Zuckerberg's March promise to find other apps like Cambridge Analytica — i.e., ones that collected data not just from Facebook users who signed up for the apps, but also all of their friends. That's the tactic that allowed Cambridge Analytica to have access to the data of "up to" 87 million people, thanks to 270,000 people who signed up for the app.

Facebook prohibited apps from doing this in a 2014 policy change. But apparently, per the scope of the investigation, thousands of apps could have used this tactic before that point. Whether they sold data or misused it in other ways is still to be determined.

Now, Facebook users can check if Cambridge Analytica accessed their data on a page created by Facebook. Facebook says that in the future, its users will be able to see whether they were affected by other apps on the same page.