Uppercase ‘i’ and lowercase ‘L’ letters are almost indistinguishable when written with the most of the fonts. This is a serious security and readability issue on the internet.
You may have encountered receiving an sms confirmation code like “UgIh43ea” and never be sure if the 3rd character is an uppercase ‘i’ or lowercase ‘L’. This is just a simple issue.
What if a close friend of yours with @IronMan username sends you a crucial message requesting some money or so, how would you be sure if that username is not actually @LRONMAN when written in uppercase?
Also, this is the same case for uppercase letter ‘O’ as in Orange and the number ‘0’ (Zero).
Prevention
To prevent such issues all the usernames and domain names should be written in lowercase. Otherwise, hackers may use this vulnerability for phishing attacks. Also, ‘i’ and ‘L’ letters shouldn’t be used in passwords, confirmation codes, serial numbers, IDs, captchas, etc..
Have a nice day…