Security Enhanced Linux (SELinux) is a Linux feature that provides a variety of security policies by using the Linux security module in the Linux Kernel. The security mechanisms that are implemented in the SELinux support a large number of security policies. SELinux is a set of security policies that secures the Linux at every level.
Email Spamming/Bombing is also combined with the email spoofing. If you find that your system suddenly becomes slow which checking the email, this means that someone is trying to process and send a large number of messages. The best security and preventive measure is to identify the source of the spam emails and configure your router, email client program to block the emails from that addresses.
Network Security
Many techniques are being used to monitor, protect and troubleshoot your Linux network. A large number of network monitoring tools are available and, Nagios Host and Service Monitoring, Saidar, Netmrg, Munin, Oreon, Mon and Zabbix are some of them. Zabbix monitors all the activities on your Linux network, such as network traffic flow, bandwidth utilization, resources allocation and troubleshooting.
With Nagios you can prepare a robust, manageable and capable network monitoring system including configurations, server preparation, software compilation and installation, apache security preparation and software download and extraction.
Web server Security
There are plenty of ways by which you can secure of Apache Web server.
Make sure that apache is running under it’s own user account and group.
Turn off directory browsing.
Turn off server side includes.
Turn off multiple options.
Run Mod_security.
Disable any unnecessary modules.
Lower the timeout value.
Limit the size of XML body.
Limit the concurrency.
Limit access by IP address.
Adjust the keep Alive settings.
Run Apache in Chroot environment
Securing Firewall
Firewall is a security wall or barrier that prevents a computer network or gateway computer from unauthorized access. A firewall is a facilitator and mediator at the same time and it is a combination of two network functions i.e. proxy and gateway. There are different types of firewalls that can be used in Linux such as packet-filtering, ipchains, stateful, and layered.
A good firewall is an important part of the network security. A Linux firewall turns off the unused ports and listens to the open network ports. Linux firewall is based on the net filters, which is set of loadable kernel modules. Smoothwall Express and Smooth Guardian are two commercially available firewall software for Linux.