unknown root username

hello - when i look in the mysql.user table, i see the following entry for root:

MariaDB [(none)]> select user, host from mysql.user where user = 'root' ;
+------+-----------+
| user | host      |
+------+-----------+
| root | 127.0.0.1 |
| root | ::1       |
| root | localhost |
| root | centos7.is.cc |
+------+-----------+
4 rows in set (0.00 sec)

i do not recognize the "root centos7.is.cc" one, so i changed the username.

when i did a new install on another centos7 box, this user entry was not there.

could some rogue process have left some sort of secret back-door in my system?

thank you all very much for your patience.