Lets start at the basics, what essentially constitutes - spam?
Spam is a copy of an email, which is flooding the internet, in an attempt to impose mass propaganda on the general mass, who in any other normal circumstances, would never have received it. Most spam, today, floating on the internet, is mostly harmless, but the tide is turning in, as more and more malware and spyware authors find potential in spamming. Most spam, again is mostly advertising of dubious products, information, some get rich asap schemes and / or quasi legal aids. To send spam, the sender does not incur any cost at all, except the internet access charges.
Spam, targets many users individually with email messages, that are sent directly to their personal inboxes. These email lists are created by scanning usenet postings, other mailing lists, or scanning the web for other email addresses. Here are some rules that might help you to avoid spam and thus make you a little more secure from some spam based spyware and malware applications.
#1 Most spammers generate their email lists by scanning web site forums and usenet groups for them. One thing that can be done, while you are posting on usenet groups or any other blogs or forums mask your email id with something obvious like, if your email id is something@someone.com, you may wan to post it as something[remove this]@someone.com.
#2 Never, under any circumstances reply to a spam, even if the spam email claims that it will remove you from the list, often these instructions lead to web sites that are infected by spyware trojans or they are meant to collect more information about you. Replying also confirms to the spammer that, your email is in fact used by you and is active, thus making you an open target to receive more spam and more advertisements.
#3 Incase you own a website, try not to put up your email address on the web site, instead provide a web based contact form, which forwards the information, to your inbox using a script. This way, bots turn up empty handed, since there is no email to collect from your web pages. You can use tools like QMail Spam filters and so on, depending on what server architecture your web site resides on. You can also hide your email address in anchor tags; most bots are not able to parse HTML tags, so you may be safe, but it is no guarantee.
#4 Install, and use antispam applications, some of these applications do come in the form of in-built modules, pre installed inside some antispyware applications, which scan your inbox email messages. This is a good idea, since such antispam and antispyware applications, are able to detect and remove most malware and spyware infected spam and other email, that you tend to receive.
#5 Here are some links to anti spam applications, which are available for free.
POPFile - A free spam filter, is very powerful and can very flexibly detect spams and junk emails, and efficiently delete and remove them for you. You can download POPFile from here. Other effective free anti spam applications include Spamihilator, Spamato and so on, which are freely available on the internet for download and use.