There are thousands of ports on your computer which any intruder can exploit unless they are secured by a firewall.

And these are the casual users who are wired to the internet at high speeds 24/7 but who may not be savvy enough when it comes to securing their computers.

High speed internet contamination do not always involve a virus (remember that a virus can only be triggered by another program). Preying on unsecured computer systems, there are some malicious web site owners who incorporate certain codes into their web pages which when viewed will take advantage of the security holes in your system itself or vulnerabilities in the browser.

The result could be that others can see right into your hard drive, plant a trojan in it and if they so wish, take over full control of your PC or even erase sensitive data contained in them.

Surf safely. It's also a good idea to keep the version of your browser up to date. Obviously the malicious programmers will target the most popular browser in the market. Check the website of your browser regularly to keep yourself abreast of any changes or security patches that may be available. There are also very good alternative browsers whose features may even far exceed those of the popular browser. Also, invest in a firewall program. As the name implies, a firewall is there to keep trouble out. What a firewall does will be explained more below.

No, you're not being told to turn off your computer. Rather, a good firewall program can keep the "open windows" of your computer shut. These "open windows" are referred to as "ports". These ports are basically input-output paths that certain programs or hardware use in the execution of their commands.

However unsecured ports leave an opening for hackers to gain entry into your computer. Just like an open or unlocked window inside your home, an intruder could climb right in. There are about 65000 ports available through the Windows system, so installing a firewall makes sure that these open ports are guarded and only legitimate traffic can pass through. They also prevent known rogue websites from showing up on your browser, keeping hackers and troublemakers out of your computer.

Be sure to read up though on your firewall's manual because you don't want to tighten your computer up to much to the extent that legitimate traffic cannot pass in or out. There are many tutorials in your firewall vendor's website that can teach you what are the most common ports that hackers try to exploit and how you can also customize your firewall so that traffic through these common ports can be diverted through less commonly known ports.