This is a free utility that will scan the ports on your computer to see if any are open to attack over the internet. Your ports should all show up stealth so no bad guys scanning your internet IP address will even know a computer is there. This utility requires no installation. All scanning of your ports is done from the GRC website. Check out the other utilities on this site. Lots of stuff here.
Microsoft now provides a free anti-malware utility. It is called Microsoft Security Essentials. Been hearing pretty good things about it. And have been quite satisfied with the speed of it myself. Check it out. I have been hearing it is on par with other free anti-virus programs. Of course remember, you do get what you pay for. But if you are careful and know how to avoid Malware yourself, a free solution like this could be all you ever need.
If you have automatic updates on, you have a good tool in your aresenal against Malware. It is call The Microsoft Malicious Software Removal Tool or MRT. There is not menu option to start this software. If must be run from the Start Menu. Simply select Start and Run. Then type in MRT and enter.
MRT runs once a month on its own. But it cant hurt to run it more often. This tool will remove infections that are already in your system. It supplies a list of infections it removes then you run it. Including the Conflicker worm that you have no doubt heard a lot about lately.
The website for info on MRT is: http://support.microsoft.com/kb/890830
One of the most common and easy to get hit with pieces of malware out there right now is Antivirus 2009. This malware will present you with a popup saying you have malware on your computer and you need Antivirus 2009 to remove it. Do not fall for this. This is itself a very nasty piece of malware. I have also heard of the name of this changing sometimes. I have heard it sometimes has 360 in the title. This is to fool people into thinking it is their Norton 360 software wanting them to do something. Know your anti-malware software and what it looks like when it alerts you to something.