Security is a very important feature of Linux. Virus or worms can't install themselves on Linux. But are there any trojans for Linux? Here is a myth-buster for you: THERE ARE.
Trojan is a malware which rely totally on social engineering to work. Remember the trojan horse legend of the Greeks. It was trickery and social engineering. A trojan fools you into thinking that it is something useful and you end up installing it. Any 12 years old kid can create a trojan. It doesn't take much of programming mastery. Creating virus or worm is much more complex.
A virus affects other file or program and replicate itself without user intervention. A worm doesn't require another file. It exists as stand-alone file and can replicate itself, once again, without user intervention.
No software can install itself on Linux and hence there can be no virus or worm for it. But since trojans rely upon user intervention, there exists trojans for Linux. Following are some tips (and they are not limited to Linux users) to secure up your PC:
-> Don't login as root, unless it is absolutely necessary.
-> Don't install any package if you are not sure about its origin. Check if the packages are digitally signed.
-> Keep all network-related packages up-to-date and regularly update the OS.
-> Turn off any network feature you don't require. It is not necessary to connect your laptop to any network if you are not using the network.
-> Create backups. It protects you from your own mistakes. I learnt the lesson the hard way when I accidently deleted 20 GB of priceless pictures of family and friends.
-> Use firewall to enhance the security features provided by tcpd.
-> The most powerful antivirus software ever created is your common sense. Use it.