One surprising part of my index file was a section called Contact Info. This contained the 764 names and phone numbers of everyone in my iPhone’s address book. Upon closer inspection, it turned out that Facebook had stored my entire phone book because I had uploaded it when setting up Facebook’s messaging app, Messenger.

This was unsettling. I had hoped Messenger would use my contacts list to find others who were also using the app so that I could connect with them easily — and hold on to the relevant contact information only for the people who were on Messenger. Yet Facebook kept the entire list, including the phone numbers for my car mechanic, my apartment door buzzer and a pizzeria…

Facebook also kept a history of each time I opened Facebook over the last two years, including which device and web browser I used. On some days, it even logged my locations, like when I was at a hospital two years ago or when I visited Tokyo last year.