Facebook harvested the e-mail contacts of 1.5 million new users who joined the site since 2016 and did so without their consent.

The social network has said it “unintentionally uploaded” the e-mail contacts after asking some users to e-mail passwords when signing up to the site as a way of verifying their identity — a practice widely criticised by security experts.

According to a report by Business Insider, those who did enter their password then saw a pop-up message telling them their contacts were being imported to Facebook, without asking for permission to do so first.

The incident is the latest in a growing list of data privacy breaches to hit the social network.

Facebook said the flaw had been caused by a feature which had allowed users to confirm their account and import their e-mail contacts at the same time; however, a redesign in 2016 had removed some of the language which explained this but was still uploading contacts in some cases.

“Earlier this month, we stopped offering e-mail password verification as an option for people verifying their account when signing up for Facebook for the first time,” a spokeswoman said.

‘Not shared’

“When we looked into the steps people were going through to verify their accounts, we found that in some cases people’s e-mail contacts were also unintentionally uploaded to Facebook when they created their account.

“We estimate that up to 1.5 million people’s e-mail contacts may have been uploaded. These contacts were not shared with anyone and we’re deleting them. We’ve fixed the underlying issue and are notifying people whose contacts were imported. People can also review and manage the contacts they share with Facebook in their settings.”

Facebook’s acknowledgement of the issue comes after concerns were raised by security researchers earlier this month. Security expert Bennett Cyphers, from the Electronic Frontier Foundation, said: “For all intents and purposes, this is a phishing attack” and labelled the process “downright irresponsible”.