Why do I need anti-virus software? Isn't Linux virus-free?

The Linux operating system, Unix and other Unix-like computer operating systems are generally regarded as well-protected, though not immune, from computer viruses, compared to Microsoft Windows.

There has not yet been a single widespread Linux malware threat of the type that Microsoft Windows software constantly faces; this is commonly attributed to the malware's lack of root access and fast updates to most Linux vulnerabilities.

The number of malicious programs—including viruses, Trojans, and other threats—specifically written for Linux has been on the increase in recent years and more than doubled during 2005 from 422 to 863.

There are 2 main reasons viruses are not a problem for Linux.

1. Linux is engineered in a fashion that makes it hard for viruses to run. Linux implements a multi-user environment where users are granted specific privileges and there is some form of access control implemented. To gain control over a Linux system or cause any serious consequence to the system itself, the malware would have to gain root access to the system.
2. More PCs currently run Windows, it is more worthwhile writing viruses for the Windows platform.

Although there aren't many Linux viruses out there, anti-virus software has its place in Linux. Linux virus scanners generally look for all known viruses for all computer platforms, including Windows. It can help to prevent the spred of Windows viruses to Windows users. Samba or NFS servers, for instance, may store documents in vulnerable Microsoft formats, such as Word and Excel, that contain and propagate viruses. Linux mail servers should run AV software in order to neutralize viruses before they show up in the mailboxes of Outlook and Outlook Express users. If you are going to trade files in a Windows world, you'll need to scan those files for viruses.

So if Linux malware is real, How can I avoid it?

• Did you see the numbers up there? There is not much malware for Linux. To get a virus in Linux you have to work at it, To get a virus in Windows you just have to work with it.
• Avoid being Root or SuperUser. Avoid entering your password to grant higher levels of permission to programs without being aware of having started those programs.
• Don't change any default settings with regard to networking unless you know what you're doing. If you decide to allow remote logins, for example, expect that people (people with malicious intent) will try to log in remotely and take control of your computer.
• Use strong passwords for all users. Strong passwords tend to be longer than six characters and a mix of numbers, letters (both upper- and lower-case), and symbols. Strong passwords do not contain birthdates, addresses, or words in the dictionary.
• Don't install software from untrusted sources. Don't just download and compile any .tar.gz, or run any .deb file you come across through an internet search, unless you know it can be trusted. The use of software repositories significantly reduces any threat of installation of malware. Only install software through the Ubuntu Software Center, or Synaptic Package Manager.
• Don't be dumb. That's right. A lot of security breaches come through social engineering. Don't give your password away. Don't open attachments from people you don't know. Don't be tricked into running a malicious program or script. Don't be dumb.