alt Hacker NewsTarget infamously was inferring when teenage girls were pregnant before their parents knew based on reward card data records of single merchant retail purchases.... in 2002.
Tech companies when they speak to VCs: look at all the creepy things we can infer with ooodles of aggregated data and AI to maximize targeted ad revenue, we're worth 50x what an equivalent non-tech company in our sector is valued, because of all the things we can do with all that data from all those people together
Tech companies when they speak to their customers: oh you're so silly to even ask about privacy, what possible utility could there be in that single isolated variable?
Accidentally inferring. They were using basic machine learning to send coupons for predicted future purchases based on past purchases and general trends. And as far as I’m aware, it only happened once (or was only publicized once).