Strange messages in syslog

[Gain Paolo Mureddu]

   Hi all... Maybe I'm being too paranoid, but I just wanted to know 
what may be going on if I have a lot of messages in /var/log/messages 
about root sessions being opened and closed very quickly, for instance:

Mar 23 16:55:01 Blackhawk crond(pam_unix)[6028]: session opened for user 
root by (uid=0)
Mar 23 16:55:01 Blackhawk crond(pam_unix)[6028]: session closed for user 
root

As you can see the session lasts less than a second. What does this 
mean? Are these processes that require root access that open the session 
and as soon as these services are done, close it??

Thanks!

PS: I know this may not be the best place to post this, if so, what 
would be the best place to post this?