unknown groups and username?
 

I see that owner:group of some directories in /home has changed to 510:506.
May I know why and how does it happened?
What is that owner and group represent?

A user who was removed from the system?

check the /etc/passwd and /etc/group what user and group refer by these numbers

Perhaps, you would have deleted the user accounts but not their home directories.

I checked both /etc/passwd and /etc/group 510 & 510 doesnt exit

sorry typo ; I meant 510 & 506

And who looks after the box? Have user accounts been deleted?

I am the admin right now for the box
Nobody deleted any user account before, They do not have ROOT access to the server

I think I found the answer :

Previous admin deleted the username from WHM but not from the linux box; so the user's folder still remain in /home.
That's why the owner:group is with unknown number

Pls correct me if I am wrong

That's what I suggested all along ;}