One of the questions that I get asked the very most is 'Now that I've cleaned all of the spyware off of my system, how do I prevent it from re-infecting me?'. There's no end-all-beat-all prevention method, but there are steps that you can take.
- Update Windows. Getting all of Windows' security updates is paramount. If you're running Windows XP, then you should definitely install Service Pack 2 if you don't already have it. SP2 has been out for some time now, and so many of the kinks have been ironed out. There's a host of security fixes for many aspects of XP that do a great job of preventing much of what is out there from infecting you. You will need to run Windows update again even after you install SP2, because there are updates even newer than the latest service pack.
- If your on broadband, use a router! Being directly connected to the internet is probably the single biggest security risk there is. Sasser and Netsky spread like wildfire to broadband users because they were wide open to the web. A lot of spyware infects you very similarly to a virus. Having a router, even if you don't have more than one computer, is a definite plus for more than one reason. First, your computer no longer directly talks to the internet. It sends the requests to the router, which then sends them to the internet, the internet then talks to your router, which routs the appropriate traffic to your machine. Second, your machine gets no unsolicited traffic. From the web's standpoint, your address looks dead. Any port scanning that happens on you address will return nothing, because the router ignores any packets that it didn't request. (Yes, you can set up your router to forward stuff to you, but you only need that in special circumstances) Software firewalls are flaky, (waaaayyyy too many headaches with 'em) so just get a router.
- NEVER install anything that a website asks you to, unless you KNOW what it is!! If you get some prompt when you go to a site that asks you to install some ActiveX thing, and you don't recognize it, then DON'T INSTALL IT! One sure-fire way to tell it's bad is if when the prompt appears, instead of the company or program name, it displays a legal disclaimer. Just be very, very careful about what you let any websites install. (Examples of GOOD things would be Macromedia Flash, The Windows Update control, eBay's picture uploader, etc)
- BEWARE of file sharing programs! Almost every single one out there comes packed with adware. Gator comes included with many, and while that's a more 'legit' one, it's still bloody annoying. Kazaa is the easiest example. You install it, it installs loads of spyware onto your machine. If you remove the spyware using the guides on this site, Kazaa will no longer work. If you reinstall Kazaa, or some other loaded program, you will re-infect yourself. LimeWire doesn't come with any adware that I know of. Use it.
For the most part, that sums it up. Staying on top of Windows updates (check for them every couple of weeks) is the best way to prevent infection from a virus-like malware item, and being careful about what you install is good advice for the rest. If you're still not feeling secure, go and get FireFox. Any adware out there now tries to infect IE because it's what everybody uses. If the majority of people get FireFox, then it may become targeted, but until then you should be pretty secure with it.