Nginx 1.8.0 - checking generally security

Hello,

i am using a digitalocean lamp stack on ubuntu 14.04.2 and Nginx 1.8.0

At var/log/nginx i see many error log files 1, 2, 4 ,5 e.t.c. is it normal ? also owner and qroup of this files is: www-data:adm
i am checking security genearally...

Thanks a lot.
George