Comodo has a free, modern, easy to use anti-virus program for various GNU/Linux distributions including Ubuntu 12.04.x.y 32 and 64 bit LTS. I just downloaded and installed it including the post-installation script. I am doing an anti-virus scan now. The graphical user interface is intuitive and it is very simple and easy to learn how to use. Anti-virus definition updates and updates to the Comodo anti-virus program itself are available right in the GUI and they are free of charge. Scanning for viruses is pretty slow if you have terabytes of data to scan, but it does show a window with the current scan progress in percentages and it shows how many objects are scanned and how many threats were detected along with the elapsed time for the scan and the start time. It's pretty comprehensive as a free anti-virus Linux program goes. I'm surprised that it's free because it is so features rich. There is no problem with this Comodo anti-virus program. There are no segmentation faults whatsoever. It just works right out of the box. I have Ubuntu 13.04 64 bit and it works. It is designed for Ubuntu 12.04.x.y 32 or 64 bit LTS as well as other popular GNU/Linux distributions.
This is especially excellent and it is very easy to use and it's completely free to update and upgrade the anti-virus definitions and the program itself. It's a small wonder why I switched from Microsoft Windows 7 to Ubuntu 64 bit full-time because of quality freemium software applications like Comodo anti-virus. This saves me quite a bit of money and it helps to give me some measure of relief.
Highly recommended! Go get it!