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Two related questions this week. Luke Murphy, Co Derry, asks what is spam, and Catherine O'Connell, via e-mail, asks how spam can be stopped.

The original spam is a cheap meat that was created for US soldiers during the second World War, and for the ration-hit home front. Its latter-day meaning derives from the Monty Python sketch about a restaurant that puts spam into every meal on the menu. Spam the meat is unavoidable in the sketch, and spam the emailed nuisance is pretty much unavoidable for anyone who has ever surfed. A rough definition would be: unsolicited e-mail sent to many people (hundreds, maybe even thousands) at the same time. It is generally trying to sell you a service or a product. Spam promising to help you get rich quick is very common. The return address is very often blocked, and even if it does say something like "just send a reply with No Thanks in the subject line to be removed from list", chances are that when you do just that the email bounces back undelivered.

The people sending you the spam will have gotten your address from unscrupulous commercial sites that sell your e-mail address (along with thousands of others) to them. Even if you have never knowingly left your address on a website, your e-mail can be traced through the "cookie" trail back to your computer caused when you use the Internet. You can turn off the cookie function but most sites will not let you enter unless your cookies are turned on.

Stopping spam is very difficult. One thing that you can do easily enough is delete without opening any e-mail that arrives in your in-box that has dollar signs and advertising messages or slogans in the subject line.

After using e-mail for a while you'll generally get to recognise the format they mostly follow. Don't worry about mistakenly deleting a message from a friend. Most of your friends will not send you an email with "You too can be a millionaire - here's how" in the message line.

Many e-mail systems, particularly Internet-based free-mail, allow you to block mail from particular addresses. This is generally easy but can get tiresome very quickly if you get a lot of spam.

Telling your Internet Service Provider about a particularly virulent spammer may lead to it refusing to handle any more mail from that source. Overall you'll probably find that deleting them as soon as they arrive in your in-box is the easiest solution. You can get more information on spamming at http://mail-abuse.org/rbl/.