By default, users of the Venmo payment service allow Venmo to mine their transaction data and share everything except the payment amounts. Venmo has chosen to exercise this liberty by providing a Web interface though which anyone with Internet access can download the transaction data — no authentication necessary!
It turns out that some people use the text fields in which one can document the reason for the payment and send a comment to the recipient as opportunities for other modes of discourse.
“A Privacy Researcher Uncovered a Year's Worth of Breakups and Drug Deals Using Venmo's Public Data”
Samantha Cole, Motherboard, July 17, 2018
Payment exchanges accumulate in a public feed, where people thought it was hysterical to write things like “money for drugs” or “sexual favors” for otherwise-innocuous payments. …
It's not so much the exposure of the intimate details of your life, … but that each transaction is just one data point in a massive web of knowledge companies like Venmo are building about us. And once they know who we're closely connected to, what we buy, and when, that's an immensely valuable dataset for companies to use in targeting your future decisions.