I would like to know at what level virus effects unix based system ? and is it necessary to have a anti virus for linux bcoz i see most distribution of linux doesn't include anti virus , although i know there are a few out there ... Anyway, it goes down to 1 question , do i really need an anti virus for my " personal " computer that runs a Webserver ... thx

As far as my knowledge goes, there are no known viruses for linux. So, rest assured. You don't have to worry about having/not having an anti virus installed.

There are several viruses out there for Linux; most of which are quite benign or proof-of-concept. Search google for “Linux virus” for details.

Linux has several intrinsic defences against viruses; email attachments cannot run themselves automatically when the email is opened, a file must deliberately be marked as executable before it can be run, for example. Furthermore, it's very rare for an untrusted executable to be run as root, so it only has local user permissions, and can't mess up your system (even if it can get at your data; a regular user typically has write access to no more then four or five executable files, which rather stops viruses from spreading too far).

However, I would definitely install something like ClamAV if you're either running an email server for Windows users, or serving up any type of executable files on a web or FTP server. I shouldn't worry about your server becoming infected; being rooted is a much more serious problem. (Look for chrootkit; you should download and run it occasionally).

Well..

I would say viruses aren't as much of a concern as "hacks" are.

I would try and get as good a firewall is possible for web serving applications (I.E, Squid Reverse Proxy)

From there, I guess you just sort of have to "wing it"

A good OS if your not afraid of it, would be something like a hardened Linux that runs behind Yoper or any other distro. This allows a great security backend for a server.

Cliekid

ADSL routers themselves offer extra firewall protection against hacks.
You can block at a router level ports that you dont need or won't be using

But make sure you change the admin password of the router as they are usually set to the same.

I don't know how easy / difficult it is to hack a Linux box.
I would imagine desktop Linux are incredibly hard.

When I read some documents about Linux Server being hacked more often than Windows
the counter-argument is that they were older Linux installation (Red Hat 7.3) and very unpatched.

We all know Windows desktop are stupidly easy to hack though.

To be safe:

* dont install files from untrusted servers
* check signature if you want extra proof
* dont run program as root unless you really have to
* dont share your passwords specially root