Country music star and guitar shredder extraordinaire Brad Paisley had a hit song in 2007 that joked about the anonymity of internet interactions between people. It was called "Online." There's a dog at a keyboard with a thought bubble saying, "On the internet, everyone knows you're a dog."
Flash forward to the present, where big data compiles huge amounts of personal data about everyone via social media for sale to marketing companies. The loss of privacy is the trade-off for free social media platforms like Facebook and Google, which sell the data in exchange for customized advertising that pops up on your screen based on your click preferences.
Fintech and other sectors (think: e-commerce and blockchain) also use various forms of encryption in an attempt to anonymize, or hide personal ID information, for security and sometimes nefarious purposes. The practice of using data mining within big data and social media to essentially backtrack, cross reference, and re-create IDs of selected users is known as De-Anonymization. While this furtive domain is filled with bad actors and not just Nicholas Cage-type illegal activity that violates privacy rules, De-Anonymization can also be a critical law enforcement tool for decrypting and identifying drug smugglers, pedophile traffickers, nuclear arms salesman on commission, and others...using the internet and anonymity encryption to hide their crimes.