What antivirus programs are available?

As an alternative to proprietary antivirus solutions like Symantec AntiVirus (non-free payware) and Avast AntiVirus (non-free freeware), you might consider ClamAV, which is free open source software. You can get it in Ubuntu by installing the clamav package. If you want a GUI for it, you can install clamtk. You can install packages in the Software Center or using apt-get from the command line as others have suggested (as well as other methods).

Its good to install anti-virus if you are dual booting or sometimes scan infected pen drives. The best option will be to use free Bit-defender for Linux. You must be knowing that Bit-defender one of the best or the best.

Link: Antivirus for Linux - Bitdefender Antivirus Scanner for Unices

Go To this link and choose 'Request a Free License (for personal use only)' from left hand side menu. You have to fill a form for license and they will send you a key and location to download anti-virus for your system.

After downloading:

Open terminal and go to location where you downloaded.

Make executable and change permission (You can use full name also I used asterisk alternatively)

chmod u+x BitDefender-Antivirus-Scanner*

Install (You can use full name also I used asterisk alternatively)

sudo ./BitDefender-Antivirus-Scanner*

The License page will open in terminal. Keep pressing space-bar till you reach end and than it will ask you to ACCEPT it. Just write

accept

And Press ENTER

Finally it will ask if you want to install GUI pack as well. Write

y

And press enter

Run it like any other application on Ubuntu. When you open it there will be an option to 'SET A NEW KEY' press it and copy the key you got in E-mail.

Bit-defender will be up and running with an year license and don't forget to Update it. There is an option in program to do so automatically.

July 22 2019: Avast for Linux seems to have been discontinued.

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You can use Avast for Linux.

You can download it free from the Avast for Linux web page.