For the anti-virus/anti-malware scanner, one of the best which is also easy to install is Bitdefender. To request a FREE License for home use (for the professional version of the software), you may contact them here. For more information on this (including installation instructions), click here. The type of security threat related to Linux is more of a concern when using Linux as a web server or mail server that allows communication to other computers in the network that are Windows based rather than Linux based, and the Windows based computers may get infected. If you run the program "Wine" within Linux to run Windows programs, it is possible for those Windows programs to be infected with Windows viruses, especially if they are any type Internet gaming program or a communications type program such as an Internet browser. Except for running programs within Wine, I have never heard of a home user ever getting his/her Ubuntu Linux computer infected with any viruses or malware. (I repeat---not a single instance in this world.) So, in general, running an anti-virus scanner on a home computer running updated Ubuntu Linux is basically useless.
NOTE: In addition, at this link is an article showing a unique way of ridding a Windows computer of viruses using a 32 bit version of an Ubuntu install disk ("live CD"), even if the computer doesn't have Ubuntu installed on it. As long as the computer is compatible with the 32 bit version of Ubuntu, it should work.
Therefore, many (or probably almost all) Ubuntu users may not see much of a need (or actually any need at all !) for scanning their files, but there is a some possibility of receiving viruses/malware as attachments to your e-mail. Viruses/malware may not bother the Ubuntu system, but they might infect your friend's system (if he/she is running Windows)---if you should forward that e-mail to your friend. Perhaps in some cases you would like to scan your e-mails before you forward them to others whose computer systems are not so safe as yours. Bitdefender normally just scans your Home Folder (by default), which is where you will typically have your various personal files stored and your e-mail.
Another advantage to this anti-virus/anti-malware scanner is the fact that you can have it scan the Windows sections of your hard drive, and any especially bad viruses or malware (especially rootkits) that force Windows to protect them from detection by anti-virus and anti-malware scanners, are helpless when scanned from Ubuntu. As long as the scanner has the signature of the malware in its database, the virus or other malware will generally be found. Ubuntu can see (both read and write) to the Windows portions of your hard drive (but Windows cannot even tell that the Ubuntu section of your hard drive exists). Files (including viruses and other malware) on the Windows side can easily be deleted by Ubuntu, when they are normally protected from deletion by the Windows operating system itself when Windows is operating.