A virus cannot, a hacker can. Two different things there. Can a hacker get
into your linux box? A very good one can, especially when the hacker uses
Linux/Unix to hack into any O/S there is. A virus what can turn a window box
into a zombie. A zombie is a system that has been turn over to spread spam, to
host a porn site, and what ever the author wants it to make your system do in
windows world. Yet, in linux and Unix world. A Zombie is a process that has died
but has not yet relinquished its process.
In the Linux world it is a very hard process to make your Linux/Unix box a
slave. I only seen a security post once for ubuntu and for all linux systems.
It was a hole in the firewall that allows a hacker to peep at your system. That
hole was closed so fast that a security up date was done at once. A new firewall
was in place and linux world resume. Try to get that from MS.
Most hackers in the linux/unix world do not care for a small user. Their main
goal is to poke holes into windows security.