A lot of chess.com information is public (by default) if you know someone's profile. Stuff a couple million email addresses and phone numbers into the "find friend" API and all you need to get profile information is the associated account username.

Chess.com should probably prevent scraping, but as we can read in just about every comment thread about LLMs/Cloudflare/Anubis/Go-away, that's not as easy as it sounds these days.