Consequences of updating packages in CentOS

Hi Friends

When I update packages in CentOS6 using yum command will it cause any damage to my server ? , I am using apache webserver, tomcat server and mysql servers on the same. If it effects the performance what precautions should I take to avoid such damage.
acutally I am trying to install packages as below
yum install mod_security mod_evasive
but getting

[root@webserver ~]# yum provides mod_security
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
Warning: 3.0.x versions of yum would erroneously match against filenames.
You can use “*/mod_security” and/or “*bin/mod_security” to get that behaviour
No Matches found
[root@webserver ~]# yum install mod_security mod_evasive
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
Setting up Install Process
No package mod_security available.
No package mod_evasive available.
Error: Nothing to do
[root@webserver ~]#

I guess if I update this I can able to install but afraid that it may lead to package issues etc.

Please some one help me out in this case.

Thanks
Kiran.

Hi

Configure Epel repository first and then install those two packages

look at the below link for installing epel repo

http://www.tecmint.com/how-to-enable-epel-repository-for-rhel-centos-6-5/