Hi all,
I am very new to Linux.

Linux Kernal is open source.
Will this feature be not easy for Virus writers
to write Virus and spread over all Linux Systems?.

Even without the Windows Source code,today hundred thousand
of Virus are written.
Every Virus writer aim is to attack the maximum number of
systems. As Windows has conquered the world desktops,
all virus were written for it and still continues.
Now Linux Users are increasing more and would
grow more in the near future.
Sure, the intension of Virus Programmers will turn to
Linux Sytems.
Then how can Linux be secured?
I also heard that a very few virus have been found on
some Linux systems.

There have been a lot of discussions regarding this issue. Use the search facility on this website and you will find a lot of threads which can give you some answers to your question.

like has been said: search

however, I'm gonna give you a short answer:

no.

virus won't run rampant on GNU/Linux like it does on windows. Here's why:

(1) Tighter ports. Windows opens a gazillion ports you don't know about (and it most likely is reluctant to tell you that it does it and *why* it does it).

(2) Permission bits: most programs can only be modified by root, which limits what the virus can spread to.

(3) It's open source. This means that security flaws are fixed faster than microsoft makes public statements.

(4) Smarter users. There are (relatively) many more people using GNU/Linux than windows that knows basic security tidbits (and generally are sceptical of `automatically download and install Evil Malware Crap version 0.02 from teh l33t h4x0r k1dd13')

Here are some tidbits of "Security" information

No system is 100% secure
No system is 'out of the box' secure. Linux is better out of the box than windows, but both are vulnerable.
Linux pro-actively fixes security and bugs. Windows waits until users complain that a bug exists.
For Linux, fixes are usually release in a few hours. Microsoft may take a week or more to issue a bug fix.
Generally virus creator are using linux due to the 'security' it provides. So why would they try to screw up there own machine

Open source kernel. Will this feature be not easy for Virus writers to write Virus and spread over all Linux Systems?.
Well, NT4 source was release on the Internet a few years back, so all the source code is out there. It may take longer to code a virus for MS, but as you stated the intension of a virus programmer is to effect the most system. Also it is probably a personal hatred of MS. I know I hate MS.

Here you go. Now write me a virus/worm for Linux.

How about viruses and worms?
# Basic Linux security and virus info
The Virus Writing HOWTO reference: Should I get anti-virus software for my Linux box?
Unusual network activity? chkrootkit is a tool to locally check for signs of a rootkit
Linux Questions Security references
Security Help Files
Linux Administrator's Security Guide
Security Focus
Linux Security
Firewalls and Security

Personally, its a preference you have to decide on.

Windows, 'can' be secure - if you know how to secure it. Out of the box, it's rubbish.

Linux out of the box is quite secure for a home desktop... if you know what your doing, it can be fort knoxx.

Linux, i doubt will ever have as many viruses as MS, because - most virus writers, etc hate MS, so they wish to attack their OS.

(5) Linux/*nix is forked to Hell. There are MANY MANY versions, with each using many many different versions of typical software. *nix is a moving target, constantly evolving. Kinda hard to hit a moving target.

Note that the number one threat isn't a system itself but it's applications. Coders need to be aware of security implications, preferably during the creation process.

Security by obscurity never worked.
.

Security more depends on your skills than OS.

Good MS admin can well protect windows xp but will fail with linux not knowing the system.

Security essentaially boils down to your mind set and physical access to the box with any operating system. Knowledge of how the OS works and why is much easier to understand and control in *BSD / Linunx /*nix. Tons of local documention (info, man), once you get used to it.

No one stated Linux was obscure by nature. I was stating that it was harder to target Linux machines with viruses and such because of the many forks and variations...that has nothing to do with obscurity.

How many viruses have been observed attacking and propagating against Linux machines? A few...I can count the ones I know of on one hand. Why so little? Many linux flavors and many different versions of applications.