Chupadados , a feminist online cyber-security guide, is designed to answer exactly those kinds of questions in order to arm consumers—particularly women—with the information they need to safely navigate the growing world of Big Data, in which the dominant business model is to scrape information about users from profiles, private messages, and tracked browsing habits, to sell to advertisers. In a survey of four popular menstrual apps the Brazil-based team of activists, writers, and technologists behind the project found that most rely on the production and analysis of data for financial sustainability. In other words, they make money off information about users' bodies and habits gathered from their profiles on and interactions with the app.

The information that we give to menstruation apps—smart phone programs that tell you when to expect that time of the month—is some of our most intimate. Still, period trackers are among the most popular health apps, with over 200 available in the App Store. So, how are we supposed to know which one is safest—which won’t sell our data to ad companies, leak it, or share it with laboratories?

And for many of these apps, the guide notes, users aren’t just tracking their periods and ovulation: “Monitoring your cycle using a menstruapp means telling the app regularly if you went out, drank, smoked, took medication, got horny, had sex, had an orgasm and in what position, what your poop looked like, if you slept well, if your skin is clear, how you feel, and if your vaginal discharge is green, has a strong odor or looks like cottage cheese.” In addition, depending on your privacy settings, the app may also know things like your location and browsing history.

As is the case with Facebook and many other apps and social networking sites these days, that data is then used to create consumer profiles for use in targeted ads. And because everyone knows that no one actually reads the terms of service before clicking “I Agree,” the Chupadados team lays out the need-to-know info in each. Glow, which has over 3 million users, the guide notes, builds-in the ability to share data with third parties, use data to inform users about products, keep data even after users have deleted the app, allow companies that have contracted Glow for targeted advertising to use embedded cookies to learn about its users, and in only some cases make that data anonymous.