1. Make sure your firewall is turned on. A firewall restricts data coming into and going out of your computer to zones that it trusts. In other words, if data comes from somewhere your firewall doesn't trust, it will be blocked. Some products have a firewall built in.
2. Make sure you update your software. Microsoft, along with some other software producers, provides automatic updates to its software to plug any gaps that could be exploited by hackers. Make sure your computer automatically looks for updates to download, particularly for Windows.
3. Get good antivirus software. Before you even connect to the Internet, make sure you have anti-virus software installed and operating correctly. And when you do connect to the Net, the first thing you must do is update this software to get the latest virus definitions so you are protected against the latest threats.
4. Apart from viruses, the other major threat to your computer is from spyware. Get anti-spyware software and keep it updated. Scan your computer using this and anti-virus software regularly.