AVG Free is a version of the AVG anti-virus software which is free for private and non-commercial use.
There is also other anti-virus software for Ubuntu.
There is no offical graphical interface available for the current Linux versions of AVG, but there is a free, third-party one called AVG-GUI.
Install AVG Free
Note: If you are using a 64-bit version of Ubuntu, you may need to install 32-bit compatibility packages. See MultiArch.
Download the deb package from http://free.avg.com/us-en/download-free-all-product and install it.
Run daemons at boot or on-demand
By default, the AVG package sets up several daemons to start when the system is booted. If you only run scans occasionally, you may not want to run the daemons all the time. In this case, you can disable the daemons' automatic starting by running:
sudo update-rc.d avgd disable
Then, when you want to run a scan, start the daemons by running:
sudo /etc/init.d/avgd start
You can stop the daemons afterwards by running:
sudo /etc/init.d/avgd stop
If you decide later that you want to run the daemons at boot again, simply reinstall the package.
Update virus definitions
After installing the package, you should update the virus definitions by running:
sudo avgupdate
Scan files and directories
You can scan files and directories on-demand by running avgscan. Refer to the avgscan man page for details. A thorough, "paranoid" scan, storing the report in a file, might look like:
avgscan -aPcijk -r /tmp/avgscan.log /path1 /path2