Linux Virii

question;
how is linux affected by virii, and how does it combat them?

No operating system is immune to viral infection, but Linux in general has several security measures (UNIX permissions, the actual file hierarchy, software delivery methods, etc) and many of its developers follow in their example when writing applications. It is for these two reason that it is much more secure beneath the surface than something the likes of Windows. This thread is likely to bring about a huge flame war with would-be evangelists using terms like 'security through obscurity' and 'vulnerability disclosure', but as it stands Linux is relatively safe and sound. To answer you questions a little more, there are several security bulletins (Linux Security being a popular one) and a few anti-virus programs (Clam-AV for instance) out there.