Linux uses root access to to control what changes are made to the system and keep the system safe.. This means that any given user can't make administrative changes that affect the whole system and allow the virus to propagate and deliver payloads. On some Linux distributions other then Ubuntu, you have to log off and then log back in as the root account to make system-wide changes. This got very annoying to the user, having to log out and log back in all the time, and it was a security flaw because if someone knew the root password they could do anything. So, as a result, many people stayed logged on as root and used it as their account for daily work. Then, when a virus came along, it was not a good day for them.
Ubuntu handles this problem by disabling the option to login as root by default at the login screen, eliminating the security risk. Then, to make any system-wide changes you temporarily switch to the root account using the
sudo command, do what you need to get done, and get back. This is a lot more secure way to handle it and much less annoying to the endi user. If you want to enable the root account for some reason, you can do so by running
sudo -i and
sudo passwd root and setting a password for the root account, if you prefer handling administrative tasks this way.
People are a lot less likely to write viruses for Linux for this reason. If they know that it won't have as much effect, they are more likely to spend their time targeting a different operating system. Linux is also a lot harder to write software for and less popular then windows, and hackers tend to pick the platform where their virus will propagate and have the most effect. All software that goes into the Software Center is screened, so you can download from there knowing it will be safe. Be careful when adding third-party software sources to your system and installing packages from places other then the software center that you don't know much about. Use clam-av as a free antivirus scanner to scan for the few viruses that may be out there. Keep your root account disabled unless you have to enable it for some reason. Update frequently through the Update Manager to ensure you stay up to date with all security updates installed. By following these steps, you are a lot less likely target for an infection then a Windows or Mac user.