Root session opened every 3 minutes

[Neil Marjoram]

I am a bit concerned about what appears to be a login every three
minutes on my server. Can anyone help with this? Heres a bit of my log
:(host is the servers hostname)

Nov  4 08:17:54 host sshd(pam_unix)[2945]: session opened for user root
by (uid=0)
Nov  4 08:17:55 host sshd(pam_unix)[2945]: session closed for user root
Nov  4 08:20:55 host sshd(pam_unix)[2991]: session opened for user root
by (uid=0)
Nov  4 08:20:55 host sshd(pam_unix)[2991]: session closed for user root
Nov  4 08:23:56 host sshd(pam_unix)[3035]: session opened for user root
by (uid=0)
Nov  4 08:23:56 host sshd(pam_unix)[3035]: session closed for user root
Nov  4 08:26:56 host sshd(pam_unix)[3205]: session opened for user root
by (uid=0)
Nov  4 08:26:57 host sshd(pam_unix)[3205]: session closed for user root
Nov  4 08:29:57 host sshd(pam_unix)[3249]: session opened for user root
by (uid=0)
Nov  4 08:29:57 host sshd(pam_unix)[3249]: session closed for user root

Thanks,

Neil.
-- 
Neil Marjoram.
Systems Manager
University College London
Adastral Park Campus
Martlesham Heath
Ipswich
Suffolk
IP5 3RL