London, Oct 4 (IANS): Ireland's Data Protection Commission (DPC), which is Facebook's lead privacy regulator in Europe, has opened a formal investigation into the fresh Facebook data breach which affected 50 million users, that could result in a fine of $1.63 billion.

In a statement on Thursday, the DPC said: "The investigation will examine Facebook's compliance with its obligation under the General Data Protection Regulation (GDPR) to implement appropriate technical and organisational measures to ensure the security and safeguarding of the personal data it processes."

"Investigation commenced into Facebook data breach," the DPC also tweeted.

The Spanish Data Protection Agency has reportedly said it would collaborate with the DPC on the probe.

"Facebook has informed the DPC that their internal investigation is continuing and that the company continues to take remedial actions to mitigate the potential risk to users," the commission added in the statement.

In the biggest-ever security breach after Cambridge Analytica scandal, Facebook last week admitted hackers broke into nearly 50 million users' accounts by stealing their "access tokens" or digital keys.

This allowed them to steal Facebook access tokens which they could then use to take over people's accounts.

Access tokens are the equivalent of digital keys that keep people logged in to Facebook so they do not need to re-enter their password every time they use the app.

US Senator Mark R. Warner has also called for a full probe into the incident.