Mozilla Audited Period Trackers. Most Failed Hard.
What happened
Mozilla Foundation, working with Harvard's Berkman Klein Center, audited six popular period-tracking apps for privacy practices. Astrology-themed app Stardust bombed with a 2/10, caught sending reproductive health details — birth control type, pregnancy status, symptoms — to third-party trackers before users even entered anything. Nonprofit-run app Euki, by contrast, aced it with a perfect 10/10: no account, no data leaving the phone, PIN protection, and even a decoy screen.
Why this matters
Reproductive health data is uniquely sensitive — especially post-Dobbs, where cycle and pregnancy data can carry legal risk. Most people assume a health app is, well, private; this audit shows that assumption is often dead wrong, with data routed to ad platforms and unnamed third parties.
The slightly cynical read
Stardust's whole personality is astrology and vibes, and it turns out the real horoscope was 'your data belongs to RudderStack now.' Meanwhile the actually private app is a scrappy nonprofit with zero marketing budget — because of course privacy doesn't monetize as well as surveillance does.
What to watch next
Expect app stores and regulators to face pressure to require clearer health-data disclosures, and for competitors to scramble to publicize their own privacy scores. Don't be shocked if Stardust quietly rewrites its privacy policy within the month.