In Linux, most people don't use anti-virus software. The reasoning is simple; there aren't many viruses for Linux, and most of them are old and don't work well any more. There are some instances, however, where such software is desirable. One of the primary ones is networking. While Linux will not be affected by viruses, it can still transmit them to other computers. If you have a network with windows computers, your linux computer can allow viruses to infect them. In this case, antivirus software is a good choice.
Enable the Universe Repositories
Click on System > Administration > Software Sources. You may need to type in your password. Once it opens, make sure the check box next to "Community maintained Open Source software (universe)" is checked, and click close. You will be prompted to reload the package lists, just click on Reload.
Install Clam AV
Click on System > Administration > Synaptic Package Manager. In the search box, type in "clamtk". You should see a package named "clamtk". Click on the white box next to it, and click on "Mark for Installation." If you get a dialog window asking to mark additional required changes, click "Mark." Next click on "Apply", and install the software. Once it has finished, you can close Synaptic.
Setup Clam AV
Open up the Clam GUI by clicking Applications > Accesories > Virus Scanner.
Run the Setup Wizard
From Clam, click on Advanced > Rerun AV Setup Wizard. Click on System Wide, then click on Save, then quit.
To let Clam run updates and scans automatically, you can click on Advanced > Scheduler. Scan options let you configure if and when you want Clam to run a virus scan. Just set the time and click add. You can also choose whether to scan your home folder or your entire computer.
Antivirus Signature options let you configure if and when Clam automatically updates its virus definitions. Again, just set the time and click add.
Since, in general, Ubuntu does not get computer viruses, System76 does not recommend the use of Clam AV to normal home users. However, if you have a network with windows computers, Clam AV can help keep your entire network safe. In addition, since servers are usually connected to the internet, and windows computers may connect to them, Clam AV can help insure that visitors to your server do not get viruses from your server, and may help maintain the integrity of your server.