A note on virus and spyware scanners:
Common sense, and intelligent use of the internet, will prevent more virus/spyware infections than a virus scanner ever will. I'm not saying you
shouldn't install a scanner, but there really isn't any
need to do so as long as you adhere to the following rules (which in my opinion are nothing more than common sense, and good computer practice):
1. Don't use obsolete operating systems (ones which are no longer receiving security updates).
2. Always keep your operating system updated with the latest patches/hotfixes/etc.
3. Use a firewall - Windows XP has one built in, as I imagine do most builds of Linux nowadays (not 100% sure on that). You don't need a third-party piece of software as long as you keep your operating system up to date.
4. NEVER open email attachments you weren't expecting. And if you were expecting them, ALWAYS visually inspect the email and the attachment to make sure it is legitimate.
5. NEVER browse to dodgy internet sites - the most common way (by far) of picking up a virus infection is by downloading crap from porn sites, warez sites, or the dodgier P2P networks. It's just asking for trouble.
In all the time I've been using a computer, I have *never* contracted a virus (depite having been emailed several), and nowadays I run quite happily virus- and spyware-scanner free without a problem.
Just my two cents anyway
