Facebook on Wednesday admitted that Netflix and Spotify were able to access user messages.
Shares fell about 6.8%, wiping out $22 billion of market value.
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Facebook shares were lower Wednesday, down 6.8% at $133.94 a share, after the company said that other companies, namely Netflix and Spotify, were able to access user messages.
The selling wiped out $22 billion of market value, dropping its market capitalization to $319 billion.
"Did partners get access to messages?
Yes," the company wrote in a blog post.
"But people had to explicitly sign in to Facebook first to use a partner's messaging feature.
Take Spotify for example.
After signing in to your Facebook account in Spotify's desktop app, you could then send and receive messages without ever leaving the app.
Our API provided partners with access to the person's messages in order to power this type of feature."
A Spotify spokesperson told Business Insider that it cannot currently read users' private Facebook messages and that there is no evidence it has ever accessed them.
Wednesday's selling comes after shares had a rally off their November lows, gaining as much as 16%.
Facebook's stock has been hit hard in recent months, falling more than 40% from its July all-time high of $218.62, as the company has dealt with the fallout surrounding the Cambridge Analytica data scandal and the hack of and the hack of 30 million users' sensitive data.
Alongside its second-quarter results in July, Facebook said that revenue growth rates would decline by "high single digit" percentages in the coming quarters.
In October, the social-media giant reported the number of daily active users were flat compared to a year ago.
Facebook was down about 20% this year through Tuesday.