Facebook Corrects Bug That Exposed Email Addresses, Phone Numbers Of Some 6M Users

The good news: The Facebook Security team snuffed out a bug that exposed some 6 million Facebook users’ email addresses and phone numbers. The bad news: The bug was active for about one year before being discovered and dealt with.

Facebook posted the following note on the Facebook Security page Friday:

At Facebook, we take people’s privacy seriously, and we strive to protect people’s information to the very best of our ability. We implement many safeguards, hire the brightest engineers, and train them to ensure that we have only high-quality code behind the scenes of your Facebook experiences. We even have teams that focus exclusively on preventing and fixing privacy-related technical issues before they affect you.

Even with a strong team, no company can ensure 100 percent prevention of bugs, and in rare cases, we don’t discover a problem until it has already affected a person’s account. This is one of the reasons we also have a white hat program to collaborate with external security researchers and help us ensure that we maintain the highest security standards for our users.

We recently received a report to our white hat program regarding a bug that may have allowed some of a person’s contact information (email or phone number) to be accessed by people who either had some contact information about that person or some connection to them.

Describing what caused the bug can get pretty technical, but we want to explain how it happened. When people upload their contact lists or address books to Facebook, we try to match that data with the contact information of other people on Facebook in order to generate friend recommendations. For example, we don’t want to recommend that people invite contacts to join Facebook if those contacts are already on Facebook; instead, we want to recommend that they invite those contacts to be their friends on Facebook.

Because of the bug, some of the information used to make friend recommendations and reduce the number of invitations we send was inadvertently stored in association with people’s contact information as part of their account on Facebook. As a result, if a person went to download an archive of their Facebook account through our download your information tool, they may have been provided with additional email addresses or telephone numbers for their contacts or people with whom they have some connection. This contact information was provided by other people on Facebook and was not necessarily accurate, but was inadvertently included with the contacts of the person using the DYI tool.

After review and confirmation of the bug by our security team, we immediately disabled the DYI tool to fix the problem and were able to turn the tool back on the next day once we were satisfied that the problem had been fixed.

We’ve concluded that approximately 6 million Facebook users had email addresses or telephone numbers shared. There were other email addresses or telephone numbers included in the downloads, but they were not connected to any Facebook users or even names of individuals. For almost all of the email addresses or telephone numbers impacted, each individual email address or telephone number was only included in a download once or twice. This means that in almost all cases, an email address or telephone number was only exposed to one person. Additionally, no other types of personal or financial information were included, and only people on Facebook — not developers or advertisers — have access to the DYI tool.

We currently have no evidence that this bug has been exploited maliciously, and we have not received complaints from users or seen anomalous behavior on the tool or site to suggest wrongdoing. Although the practical impact of this bug is likely to be minimal — since any email address or phone number that was shared was shared with people who already had some of that contact information anyway, or who had some connection to one another — it’s still something we’re upset and embarrassed by, and we’ll work doubly hard to make sure nothing like this happens again. Your trust is the most important asset we have, and we are committed to improving our safety procedures and keeping your information safe and secure.

We have already notified our regulators in the U.S., Canada, and Europe, and we are in the process of notifying affected users via email.

We appreciate the security researcher’s report to our white hat program, and have paid out a bug bounty to thank him for his efforts.

And users who were affected received the following email from Facebook:

Dear _________,

Your privacy is incredibly important to everyone who works at Facebook, and we’re dedicated to protecting your information. While many of us focus our full-time jobs on preventing or fixing issues before they affect anyone, we recently fell short of our goal and a technical bug caused your telephone number or email address to be accessible by another person.

The bug was limited in scope and likely only allowed someone you already know outside of Facebook to see your email address or telephone number. That said, we let you down and we are taking this error very seriously.

Describing what caused the bug can get pretty technical, but we want to explain how it happened. When people upload their contact lists or address books to Facebook, we try to match that data with the contact information of other people on Facebook in order to generate friend recommendations. Because of the bug, the email addresses and phone numbers used to make friend recommendations and reduce the number of invitations we send were inadvertently stored in their account on Facebook, along with their uploaded contacts. As a result, if a person went to download an archive of their Facebook account through our download your information tool, which included their uploaded contacts, they may have been provided with additional email addresses or telephone numbers.

Here is your contact Information (inadvertently accessible by at most one Facebook user):

______@______.com

We estimate that one Facebook user saw this additional contact info displayed next to your name in their downloaded copy of their account information. No other info about you was shown, and it’s likely that anyone who saw this is not a stranger to you, even if you’re not friends on Facebook.

We recognize that mistakenly sharing contact info is unacceptable, even if you are acquainted with people who saw these details, and we’ve taken measures to prevent this from happening again. For more information on the bug, please read our blog post.

All of us at Facebook take this issue very personally. We appreciate your ongoing use of Facebook, and are working every day to deliver the level of service you expect and deserve.

Thank you,

The Facebook Team

Readers: How many of you received similar emails?

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