Mod_security is an apache module that helps to protect your website from various attacks. It is used to block commonly known exploits by use of regular expressions and rule sets and is enabled on all HostOnNet servers by default.
In any case, if you want to disable it, you can do it from cPanel
Login to cPanel, under the Security section, click on ModSecurity.
On next page, you can see the list of domains and on/off status. ModSecurity will be ON by default for all your sites. Click on OFF button to disable ModSecurity