Warning: mysql_connect(): mysqlnd cannot connect to MySQL 4.1+ using the old insecure authenticat
当mysql版本< 5.1时，php版本为>=5.3时，mysql_connect()会显示的是如下错误：
Warning: mysql_connect(): Premature end of data (mysqlnd_wireprotocol.c:554) in D:WwwRootAutoDialmysql_connect_test.php on line 7 Warning: mysql_connect(): OK packet 1 bytes shorter than expected in D:WwwRootAutoDialmysql_connect_test.php on line 7 Warning: mysql_connect(): mysqlnd cannot connect to MySQL 4.1+ using the old insecure authentication. Please use an administration tool to reset your password with the command SET PASSWORD = PASSWORD('your_existing_password'). This will store a new, and more secure, hash value in mysql.user. If this user is used in other scripts executed by PHP 5.2 or earlier you might need to remove the old-passwords flag from your my.cnf file
【解决方法】
1. 找到配置文件my.cnf（Linux，/etc/my.cnf）或my.ini（win，安装目录），打开，将其中old_passwords=1注释掉；
2.重启mysql；
3. 将mysql用户对应的密码重新设定一下（set password for 'user_test'@'{这里写你的地址}' = password('123456')）。
【原因】
有 的安装情况下，MySQL 5.0 为了和4.1之前的版本兼容，用户密码（mysql数据库的user表password字段）保存的是密码的16位hash值，而PHP5.3的 mysql驱动使用41位的密码hash值进行用户验证，所以需要让mysql中保存用户密码的41位hash值，但配置文件中 old_passwords=1的话，password()函数只能返回16位hash值。参考mysql5.0文档security章password hashing in mysql节。
转自：http://topic.csdn.net/u/20110306/12/d6f13885-da88-46c4-a37d-eae656bf65ca.html