Does Linux require an anti-virus?

Definitely. It used to be the case that Linux was not heavily targeted by malware writers for two main reasons. Firstly, the general popularity of Linux amongst home users wasn't very high. This meant hackers had a low number of potential victims and hence a low 'return on investment' for their efforts. It was always far more lucrative to attack Windows because of its large user base. Secondly, the fact that there are many variations (distributions) of the Linux OS meant virus programmers would have to create and test separate attack code for each of them. Compare this to Windows where a single virus code is capable of infecting everybody that uses the operating system. In the past few years, however, both these points have been eroded. Firstly, there is a general increase in the popularity of the OS with more and more home users adopting Linux. The fact that major computer distributors like Dell are shipping desktops and laptops with Linux per-installed is testament to this shift. Secondly, the run-away popularity of easy-to-use distributions like Ubuntu has consolidated the fragmented Linux user base. Unfortunately, this makes it easier for hackers to create a single piece of virus code that will hit millions of users.