This is what I got from logrotate.conf.
It seems by default, there will be file 5 log files a week.
After one week, it will clear older one.
In my case each log file was 50MB of size. And there are 5 instance of each. like /var/log/secure, secure.1, secure.2, secure.3 and secure.4.
This appears to be an expected behavior. Isnt it?