Log scares me

Any generic counter move?

[henry0]

I noticed in my daily sent log many thousands of such:
**Unmatched Entries**
pam_succeed_if(sshd:auth): error retrieving information about user susan : 1 time(s)

Of course user is whatever... times thousands

How should I react?

[encyclo]

Are you talking about ssh log entries? If you are the only one accessing the server via SSH, you can make the SSH daemon listen on a different port - that will help with brute-force attacks on the standard SSH port.

[henry0]

Thanks
I am not alone, another developer access it too,
but I suppose it is anyway the way to go.