Desktop Linux distributions have a distinct advantage over Windows. They are not plagued by the millions of viruses that circulate the Internet wreaking havoc on unsuspecting PC users. These viruses are designed for Windows and normally only affect Windows systems.
Despite the apparent immunity Linux enjoys, a Linux server should still have some type of virus protection. The main reason is that many of your server’s users and website visitors may use Windows. Assuming they do, any viruses shared over the Internet, especially to their email accounts, can put the entire server at risk. The viruses will most likely not execute on the Linux system, but users who unknowingly pass them through your email server may spread them quickly.
The other issue that you will want to consider when fighting viruses is spam. If you are running mail servers, you will also want to find a way to fight it. There are some tools like MailScanner that will fight spam and viruses, keeping them out of your emails. They often utilize the services in specialized tools like ClamAV, an open source anti-virus program, and Spam Assassin, an anti-spam tool.
If you are not using a mail server, viruses and spam will not be your primary security concern, but you should still use some type of security software, such as OSSEC an open source intrusion-detection system provided by Trend Micro. You should also consider a strong firewall, such as APF. With the right tools in place, you can find off just about every type of threat to your dedicated server.