Updated Backup specialist Backblaze has fixed an issue where a Facebook advertising pixel was "inadvertently" included on signed-in web pages – but users are concerned private filenames and sizes were also sent to the social media giant.
The problem was spotted by Blackblaze customer Ben Cox who protested on Twitter: "WTF? @backblaze's B2 web UI seems to submit all of the names and sizes of my files in my B2 bucket to facebook. I noticed because I saw 'waiting for facebook.com' at the bottom while trying to download a backup."
B2 is the Backblaze cloud storage service.
The company responded with a blog post that stated: "On March 8, 2021 at 8:39pm Pacific time, a new Facebook campaign was created that started firing a Facebook advertising pixel, intended to only run on marketing web pages. However, it was inadvertently configured to run on signed-in pages."
The company added that it uses Google Tag Manager to "help deploy key third-party code in a streamlined fashion." According to the post, "we removed the offending code from the signed-in pages on March 21, 2021 at 11:19pm Pacific time."
But what did you send them?
The Backblaze explanation does not fully address user concerns. A key question is exactly what data was transmitted to Facebook. The term "advertising pixel" suggests a simple request to insert an invisible graphic file on a web page, for the purpose of tracking the page view, but the amount of data sent in such a request can be extensive, since the script has access to the entire contents of the page.
A Facebook developer page explains that by default "the Facebook pixel will send button click and page metadata (such as data structured according to Opengraph or Schema.org formats) from your website to improve your ads delivery and measurement and automate your pixel setup."
Cox originally stated that "all the names and sizes of my files" were included in the data sent to Facebook by its script. The Backblaze post made no mention of this, but presuming the names of files were included, this is a more serious breach of privacy than simply tracking use of the service.
There was also an expectation on the part of users that when signed into a paid-for backup service that their interaction with the application would be private. The presence of Google Tag Manager code, which injects third-party code into a web page, potentially undermines that hope even if configured to do nothing. It is not clear from the Backblaze post whether Google Tag Manager has been removed from signed-in pages, or merely reconfigured.
This kind of problem may be more hidden in future. From the user's perspective, an advantage of client-side tracking is that it can be blocked. Google notes in its developer guidance for Tag Manager that "server-side tagging allows you to move tag instrumentation off of your website or app and into the cloud." Server side tracking, whether or not "inadvertent", is invisible to users and therefore less likely to be spotted.
We have asked Backblaze for more details of exactly what kind of data was inadvertently transmitted to Facebook.
Updated on 24 March at 11.44 to add:
Backblaze has responded to us with more information, also given in an updated blog post on the incident. The company said that only one of the signed-in pages was affected, but that it was visited by over 9,000 users while the code was active.
“If users were browsing their B2 Cloud Storage files on b2_browse_files2.htm during that period, AND clicked to preview file information, then the Facebook pixel pulled the following metadata: folder/file name, folder/file size, and the date the folder/file was uploaded,” the team said.
User account information was not uploaded. Backblaze added that “We removed the offending code from the signed-in private pages on March 21, 2021 at 11:19 p.m. Pacific time. We also subsequently removed Google Tag Manager from the private pages.” It has promised to communicate with affected users. ®