De-anonymizing Social Networks
https://www.cs.utexas.edu/~shmat/shmat_oak09.pdf
If I understood it correctly from a quick scan: by talking to the same people
across different networks (e.g. Alice is friends with Bob and Claire on both
GNU Social and Mastodon, but all of them have different and untraceable
nicknames), Mallory can figure out with high probability which account is
Alice's on the other network given a network/friends graph of both.