Spam is flooding the Internet with many copies of the same message, in an attempt to force the message on people who would not otherwise choose to receive it. Most spam is commercial advertising, often for dubious products, get-rich-quick schemes, or quasi-legal services. Spam costs the sender very little to send -- most of the costs are paid for by the recipient or the carriers rather than by the sender.

In addition to wasting people's time with unwanted e-mail, spam also eats up a lot of network bandwidth. There is some debate about the source of the term, but the generally accepted version is that it comes from the Monty Python song, "Spam spam spam spam, spam spam spam spam, lovely spam, wonderful spam..." Like the song, spam is an endless repetition of worthless text.

A zombie computer (often abbreviated as zombie) is a computer attached to the Internet that has been compromised by a hacker, a computer virus, or a trojan horse

In a survey, conducted on different computers all around the globe, it was found that 50 - 80% spam worldwide was sent by zombie computers. A zombie computer is mostly a home computer which is infected with a virus/trojan horse. Unlike the zombies of any Hollywood movie, zombie computers are not easily identifiable, they are silent workers.

David Lawrence, 43, owns such a computer, which turned into a "spam zombie" when a virus infected it in October. Five or six spammers were using his cable modem to remotely send pitches for products like Viagra and boosters for cell phone signals.

"Spammers and the people who write these viruses ... is their life so void that they feel they have to mess up other people?" said Lawrence. "To me, it's criminal."

Determining whether your PC is a zombie isn't always easy, says Fred Felman, vice president of marketing for Zone Labs, a San Francisco security software maker. Symptoms can include a suddenly sluggish broadband connection, excessive hard drive activity, an unresponsive mouse or keyboard, or bounce notifications in your inbox from people you never tried to contact. Yet you could show all of these symptoms and still not be infected.

Hackers sometimes turn unsuspecting victims' computers into zombie computers to spread e-mail across the world. E-mail recipients usually can't trace the e-mail back to the hacker.

- You can reduce your risk by installing a personal firewall and antivirus software, and keeping your Windows Updates up to date. Yet most home users remain woefully unprotected. A study conducted in May 2003 by the National Cyber Security Alliance found that two-thirds of home users did not have a properly configured firewall.

- Use filters and rules to screen unwanted mail. Filters and rules are tools within e-mail programs that identify incoming messages as spam. Spam messages are then routed to a specified folder­such as Junk Mail, Trash, or Deleted Items. The process for creating filters and rules differs slightly in each program but the basic concept is the same.

- Don't be fooled by various "phishing" schemes designed to trick you into revealing personal information. Some spam messages contain urgent requests for personal information such as bank account numbers. Frequently they appear to come from reputable institutions. Don't trust such "phishing" requests and delete such e-mails immediately. Also, it is good practice to never follow instructions to "remove yourself from the list." These removal instructions are a gimmick used to verify that yours is a valid e-mail address. If you click on it, spammers will add you to their list or sell your address to someone else. Replying in any way to a spam message lets spammers know they have found a valid e-mail address.