Linux has also proven to be a robust, stable, reliable and secure operating system. This means that linux is not affected by worms, spy ware, virus etc. which has turned out to be a major problem for most Windoze users in the corporate world these days. The worst a person can do is spend most of his time in the office reinstalling the OS after his computer is effected by a virus or a worm. Many useful man hours and money is lost in just reinstalling.Linux too has it share of virus and worms but it can effect only the users files not the entire system. Given below is an portion of wonderful blog on this subject.

Any program on a Linux box, viruses included, can only do what the user who ran it can do. Real users aren't allowed to hurt the system (only the root user can), so neither can programs they run. Because of the distinction between privileged (root-run) processes and user-owned processes, a "hostile" executable that a non-root user receives (or creates) and then executes (runs) cannot "infect" or otherwise manipulate the system as a whole. Just as you can delete only your own files (i.e., those you have "write" permission to), executables you run cannot affect other users' (or root's) files. Therefore, although you can create (or retrieve), and then run, a virus, worm, trojan horse, etc., it can't do much. Unless you do so as "root". Which it's simple to avoid doing.

One of the most talked about advantage of Linux is that LINUX IS FREE. That still the number one reason to migrate to Linux for many. Being free means that there is no per user licence for all the software as well. For example, with windows you get a terminal server. But that has a 5 user licence limit. This means that the cost is not of the OS alone. But along with it every application costs. And each time the work environment is duplicated on another machine you spend the same amount of money. With time the software is upgraded and the files from the new applications would not work on the older versions. The users are forced to upgrade. This process can always increase the overall costs the organization has to absorb in. Hence, with most commerical operating systems the cost is never a one time cost.