At some point you will no doubt receive unwanted e-mail messages from unknown senders including individuals and companies advertising their products or services. Such messages may take the form of online surveys that ask you to enter personal information. Unsolicited messages like this are known as junk mail or spam.
Junk mail may include content that is harmful for your computer. It is often used for identity theft. You should never respond to junk mail, simply delete it as soon as you receive it. Many e-mail programs have a junk mail folder where the junk mail can be directed and later deleted.
Spam filters can be used to detect junk emails and get rid of them before they reach your inbox. Many ISPs offer spam filtering as part of their service.
The BBC Webwise site provides some useful information about how to prevent spam.