Avoid using the administrator account
When you use a computer, you use a user account, whether you realize it or not. Most of the time, this is obvious, since you clicked on your user name and typed your password. Your account usually has a certain set of privileges. For a regular user account, you have limited privileges that allow you only to modify files in your own folders. Power users and administrator accounts can modify most files.
If you want to keep your computer more secure, do not use an administrator account for regular day-to-day things, like surfing the web and checking your email. If you visit a bad web site or open a malicious email, the malware will run as you. If you are an administrator on your computer, the malware will run as an administrator. While you may want to feel the power of being an administrator, this will give viruses like Trojans and rootkits an easy way to gain total control over your computer. If you limit your privileges, you limit the damage that a virus can inflict.
For the everyday things you do on your computer, use the user-level account, without administrator privileges. This way if bad things try to take over your computer, they will have limited access to the files on your computer and will not be able to take over the whole computer. If you need administrator privileges, the computer will ask you to log in as the administrator before allowing you to proceed.
Limit your use of the administrator login to updating software patches and installing trusted software from verified sources. Above all, use a really strong password for all administrator accounts. This will help to prevent damage by any viruses that slip under the radar of your antivirus software.