Right, a stupidity which I find often on forums and articles online is that Linux is a virus free OS...and the subsequent distros following with the same claim.
Due to this people often get confused whether they need an AV or not, and the reasons for having an AV, although quite valid, still leave much unanswered.
So let me clarify a couple myths about any linux distro, Ubuntu included.
1. Yes, it is possible for a virus to infect a Linux machine. And Linux virii do exist.Now, the problem here is that it is virtually UNLIKELY that YOU will get infected.
Reasons being that most viruses are meant to exploit windows faults, therefore there are very few virii which actually work on linux.
Also linux is very distro specific, each distro has its own packaging method, e.g. deb, rpm, ipk etc...
This creates another problem for the virus, it would have to be created to target a specific distro, or group of distros, thus limiting itself, windows doesn't have this problem.
Constant updates help minimize the chances that a well supported distro will be infected.
And last but not least a common Linux user is generally more experienced than a common windows user, therefore the Linux user would be able to suspect and avoid infected files with greater ease.
2. No, AV software do NOT only scan for windows virii.
They scan for any virus whose signature is in its database, and those which do heuristic scanning can scan even more, this doesn't matter what OS the virus is targetting.
3. No, you do not ONLY need an AV if you share files with windows machines. You need an AV on any machine which accesses the internet, independently of the OS.
Although it is true that if you catch a windows virus it will not affect you, but whoever you share it with, it is not the ONLY reason as to why you need an AV software.
The real-time scanning feature may be unnecessary, but a powerful AV should be installed in case of emergencies, and occasional scanning.
The scan will clean both the widows virii and any Linux virii which you might have picked up.
AV software are a must in any OS. But on Linux distros you will be using them less frequently. You do not need real-time protection, but carry out regular scans, e.g. Once a month. Both to make sure your box is clean and to keep your windows friends virus free.