Spam is unsolicited, usually unwelcome, e-mail that offers products and services that you probably do not want. The people who send spam, called spammers, usually disguise their real intent by creating a Subject text that fools you into opening the message. Subjects such as "That file you wanted", or "When will we meet" are more often than not simply trickery. The first rule is: never open a message you believe to be spam. If you cannot identify the sender or be sure the message is really meant for you, then delete it. The Preview Pane in Microsoft Internet Explorer does open the message and may trigger any malicious content. More of that in a moment, but the feature should be turned off.

Far from just being a waste of time to identify and delete spam, there are more serious consequences. Spammers do not generally know your e-mail address, they simple send out hundreds of thousands of messages to every combination of addresses they can imagine. Obviously some do not exist, but ones that do are valuable. The second rule is: never reply to spam. The spam process is automated and the sender's address is invariably fake. What it may do, however, is prove to them that you exist. They can then send more spam to you and sell your address to others so that, in turn, can send you more spam.

If you open a spam e-mail there is a good chance that it has been written in HTML, which is the language used to build websites. HTML can be very complicated, but in the case of an average e-mail message it simply contains text. Or does it? One thing an HTML document can contain is a picture, which is located on the sender's web site. When you open the document your mail program requests a copy of the picture from the sender. The sender will see your request and log your address. You might not even see the picture; it only needs to be a single dot. Again they know you exist.

More serious still is the fact that e-mail can contain attachments. This is legitimately used to send pictures, documents or any other form of electronic data; including programs. The third, and most important rule is: never, ever, open an attachment unless you are certain of its origin and content. This is the commonest route for viruses entering your system. A virus is a program that gets into (infects) your computer without your knowledge, rather like catching flu before the symptoms appear. If the program gets a chance to run it usually uses your mailing list to send copies of itself to all your friends and associates. That is bad enough, since the amount of computing time and network traffic is increased, thus decreasing it for legitimate users.

However, the virus can be malicious. Most could generously be termed mischevious, but others can do serious damage to your system: delete your data, crash the system and some are known to hijack your Internet dialup connectionso that, instead of calling your usual number, they can dial a premium rate number instead. You probably will not notice the difference, until your phone bill arrives. A recent television program highlighted the problems of people who had bills running into hundreds of pounds. Unfortunately for them, the phone companies refused to waive the bill pointing out rightly that the consumer did actually, if unwittingly, call the number.

Apart from phone bills, you need to calculate the risk to you or your business if your data is destroyed and goodwill from associates is lost. What is the simple cost of rebuilding the system in terms of time and money? There are many anti-virus and anti-spam products available. They are not terribly expensive although they do require regular subscriptions to keep up-to-date. It is no good if a product bought last week fails to recognise the next new strain of virus that arrives tomorrow.

For more information on spam and spammers see http://spamsites.org/ and http://www.spamhaus.org/.