How can I prevent being spammed through using newsgroups? 

Unfortunately spamming is one of the disadvantages of using the Internet and in particular when using Newsgroups. If you post to the Newsgroups you will, sooner rather than later, be subjected to spam. There are, however, certain measures that you can take which can reduce the amount of spam mail you receive.

A common technique you can use is to simply alter your email address. It's a simple but effective way of reducing incoming spam mail.

In Outlook Express, click on 'Tools' then 'Accounts' and select the 'News' tab at the top. Highlight your News account and click on 'Properties'. You can change your email address here. In Netscape, click on the 'Edit' menu and select 'Preferences'. Then click on the 'Identity' tab under 'Mail and Newsgroups' and look at the 'Email Address' field. You will see that your email address is there and this is what spammers use to email you with. Some people change this address, for example:

Change you@virginmedia.co.uk to you@NO.THANKS.virginmedia.co.uk

This means that spammers using this address will have any mails sent to you bounced back to them. However, this will also apply to legitimate users who are trying to email you by clicking 'Reply to sender'. One way to get around this is to notify them of the correct reply to address in your signature file, for example:

Your Name

you(at)virginmedia.co.uk
(Please remove the NO.THANKS. in the reply to address)

Please make sure that you change the domain part of your address, this prevents the spam from clogging up the mail server while it searches for the address. Also make sure that the munged domain you have added isn't a valid domain.

Be creative with your mung, and change it often as well. These steps will prevent harvesters from picking up on patterns, and possibly changing their software to defeat them. However, you should still make it obvious to humans:

DO: your-name(AT)example(DOT)com
DO: your-namZ@ZxamplZ.nZt (Replace Z with E)
DO: see_my_sig@for.my.real.address
DON'T: your-name@foo.example.com

If you decide to add a "spamblock" to your existing address, put it on the right-hand side of the @ sign. This avoids making your provider's email server handle undeliverable mail.

DO: your-name@-REMOVE_THIS-example.com
DON'T: your-name-SPAMBLOCK-@example.com

Tell folks how to de-mung your address somewhere in your message. The signature (sig) that gets added to the end of each message is a good place to do this.

DO: "To reply via email, remove '-REMOVE-THIS-' from my address."
DO: "Real address is myrealname AT example DOT com"
DO: "Replace all the Z's with E's to reply"
DO: "Send email to myrealname; ISP is example DOT com"
DON'T: "Real address is myrealname@example.com"
DON'T: Add a directly usable address in your sig, because many harvesters collect everything with an @ sign in it.

For more advice and tips it might be worth paying a visit to the following newsgroups dedicated to Internet abuse:
news.admin.net-abuse and in particular news.admin.net-abuse.email.

There are programs that you can download that monitor your access and limit certain types of material from getting through, try:

http://www.netnanny.com

Some mail clients allow you to set up filters, Outlook has this facility and will block any messages containing chosen keywords.

There are also plenty of online spam trackers that will dissect the spam mail and send abuse reports to the relevant ISPs. One of these is Spamcop, at http://spamcop.net.

This is not a service supplied by Virgin Media, but can be extremely useful for tracking the source of these messages.