This type of bug is classified as a "Photo API" bug. It was able to infiltrate photos that users uploaded but did not share with their timelines, the Marketplace platform, and the Facebook Stories feature. The bug was active from September 13th to September 25th of 2018. The widespread bug affected 1,500 apps that were built by 876 developers.
This is not the first privacy issue that has plagued Facebook and other social media platforms. In June, there was another bug that caused the privacy settings of around 14 million Facebook users to switch to public, even if they had not selected this option.
Second, with the advent of stricter privacy laws in Europe, if a significant number of people were affected in that region then Facebook could actually be subject to heavy fiscal penalties.
Facebook's posted a note saying "We're sorry this happened," a brief response that many consider inadequate. Still, there's little expectation that the bug will cause users to leave Facebook. "Even if people don't trust Facebook, as long as the value that the service provides is worth more than the cost of the privacy violations, then that may be a trade-off most people are willing to make," said Nate Elliott, an analyst at Nineteen Insights.
That said, Facebook's growth has been slowing even prior to such privacy violations. Sign-up rates have waned, and people are spending less time on the platform itself. This makes the extent to which the bugs have negatively impacted growth and usage unclear, as it is currently inseparable from already-deteriorating statistics.
In February, Chief Privacy Officer Erin Egan assigned Facebook a "B" grade when asked how much it would score on privacy issues. By 2019, the company aspires to transform this into an "A."