ecs上的mysql数据库安全吗？？

早上起来发现mysql的error日志有如下报错：
我看了下，这三个IP都是阿里云上海、杭州、深圳的

2018-05-23T01:21:20.094142+08:00 10 [Warning] IP address '106.15.76.92' could not be resolved: Name or service not known
2018-05-23T03:31:05.594699+08:00 11 [Warning] IP address '120.78.225.124' could not be resolved: Name or service not known
2018-05-23T04:17:43.325303+08:00 12 [Warning] IP address '118.31.244.58' could not be resolved: Name or service not known


我确定大半夜的，我没有使用过。账号密码也是比较安全的。请为什么感觉有人登陆了我的数据库？（或者说在尝试）