As Bloomberg reports, 533 million Facebook users’ information resurfaced on a hacker website on April 3. Cybersecurity experts have said the data included phone numbers, email addresses and locations. Facebook maintained the data was from an old leak that was previously reported on in 2019 and has since been fixed.

The leak was so big that it included the personal information of CEO Mark Zuckerberg, according to a researcher, as Business Insider reports. Cybersecurity researcher Dave Walker said Zuckerberg’s cellphone number was among the data posted for free on the hacker website.

Regulators quickly began circling. Ireland’s Data Protection Commission, the lead privacy watchdog in the European Union, has been reviewing the data dump, as the BBC reports.

The DPC’s deputy commissioner Graham Doyle said that while the data-scraping that was apparently behind the leak took place before the EU’s General Data Protection Regulation law took effect, “we are examining the matter to establish whether the dataset referred to is indeed the same as that reported in 2019.”

The Facebook users affected by the leak reportedly hail from more than 100 countries, including more than 30 million Americans and 11 million UK Facebook users.

Old data dump or not, as CNN notes, users’ phone numbers and birthdates probably haven’t changed since 2019. A worsening of the robocall epidemic is likely because the leak included names and phone numbers. Phishing is another probable risk, according to cybersecurity experts.

It’s difficult to determine whether an individual’s information was part of the leak, observes The Conversation. The original 2019 data haul was reportedly most likely due to a then-permitted use of Facebook’s service, similar to the Cambridge Analytica scandal.