Also using similar unicode characters in your username for nefarious spoofing attacks or worse -- https://labs.spotify.com/2013/06/18/creative-usernames/ https:

Also using similar unicode characters in your username for nefarious spoofing attacks or worse -- https://labs.spotify.com/2013/06/18/creative-usernames/ https://labs.spotify.com/2013/06/18/creative-usernames/ This is called a Homoglyph attack. If you accept unicode for strings that should be "unique" (eg username), there are various normalization schemes that basically convert equivalent-ish looking characters into a consistent hash. I have no doubt spam filters use this.