Major Description
When using Windows Explorer to attempt to connect to an FTP connection, it first attempts an anonymous login and then prompts the user for credentials after failure. Disabling anonymous login on the current version of Apache FTP Server returns a 530 response and immediately closes the connection, preventing the credentials dialog from appearing in Explorer and causing an error dialog to be displayed.
If the USER command is successful and the anonymous user is rejected after the PASS command is sent with a 421 response sent by the server, Windows Explorer is able to handle the login process properly. To maintain maximum compatibility, anonymous user checks should all be handled in the PASS command.