mysql用户表中的未知主机条目

Question

mysql> select user,host, password from user
+------+-----------+----------+
| user | host      | password |
+------+-----------+----------+
| root | localhost |          |    
| root | 127.0.0.1 |          |
| root | ::1       |          |
|      | localhost |          | 
| pma  | localhost |          |
+------+-----------+----------+

列主机中的“:: 1”条目是什么？这是一个我需要关心的安全问题（没有设置密码）