For a description see e.g

• http://stackoverflow.com/questions/9040771/mysql-access-denied-for-user-odbclocalhost-to-database?rq=1
• http://stackoverflow.com/questions/23950722/how-to-overcome-error-1045-28000-access-denied-for-user-odbclocalhost-u
• http://stackoverflow.com/questions/24853944/access-denied-for-user-odbclocalhost?rq=1

On Unixes, if client does not provide username (in command line 'mysql' client , or in mysql_real_connect()), the name default to current OS user. On Windows, due to incorrect way of determining the name, it always falls back to 'ODBC' (or almost always, Cygwin environment could be the one where getenv("USER") actually works)- Asked Lawrin if this is of any use for ODBC, he said no

Upstream bug https://bugs.mysql.com/bug.php?id=48371