A groundbreaking study likens social media privacy to secondhand smoke: it's shaped by those around you. We've long believed that avoiding platforms like Facebook or X (formerly Twitter) keeps your data private. This research delivers compelling evidence that individual choices alone aren't enough.
Researchers analyzed over 30 million public X posts from 13,905 users. Their key finding: content from just 8 or 9 contacts predicts a person's future tweets as accurately as their own feed.
Even if someone deletes their account or never joins, friends' posts retain about 95% of the "potential predictive accuracy" for that person's future activities, the scientists note—without accessing their data.
Flip the perspective: signing up for Facebook or any platform means "you think you're giving up your information, but you're also giving up your friends' information," says the lead mathematician.
This work probes the essence of privacy in networked societies, where personal choices intertwine with others'. In theory, companies, governments, or others could profile individuals—from political leanings and product preferences to religious views—using only friends' data, even if the target avoids social media.
The analysis of X posts identifies a mathematical limit to a network's predictive power, but it holds steady whether the profiled person is active or not, as long as their contacts are.
"You just can't control your privacy on social media platforms," the researcher emphasizes. "Your friends have a voice, too."
