By now I hope you all are familiar with some virus scan tools. These are a class of program that is always running on your Windows machine. They look at every file that comes into your machine and try to match the incoming file against patterns of known viruses. They all rely on databases on your machine of patterns which you must be sure are updated regularly. Any tool worth its salt today will "just work". You install it and it goes off regularly to update its virus lists.
Your computer most likely comes with some such tool. A few popular ones are (again I have no financial interest in any of these):
These tools are only as useful as their virus database. They must update regularly - and most require yearly subscriptions for this service. It is very possible your employer will already have you covered. Most employers have figured out it's in their own interest to make sure your Windows machine at home is reasonably safe, lest you bring viruses from home into work. Check with your local IT people and see if this is the case. This can save you the cost of a yearly subscription.
Your brand-new Windows machine comes with nothing to help you. One of the very first things you should do is install your virus scanning program. The exact details will vary by product, but all tools will start off by getting the latest virus updates and then scanning every file on your machine.
As soon as this scan gets started, you should disconnect from the Internet. You have to wait until the scan starts, because the virus tool should first go out on the Net and get its updates. You need to be connected for that. As soon as the scan begins, you can and should disconnect so you don't get infected WHILE the scan is going on. This scan will take some time -- many minutes. Time for yet another coffee break. It would not be surprising if it already finds something on your brand new machine because you were, after all, on the Net right? Your virus scanner should delete the virus. When the scanning is done, reconnect to the Net.
After the install/scan is complete, you'll see the virus program is running and has a small icon in the lower right hand corner of the screen. Do a right-click on this and you'll have several options.
Two options you want to know about will say 'Update Now' or the like (get the most recent virus updates) and maybe 'VirusScan Console' or the like. This latter will show a window maybe something like this - where you can control all sorts of options. Once in a while (perhaps monthly), you should get to this console and re-scan your entire machine again. Just in case - you can never be too safe, right?
The McAfee product has several interesting options from this right-click menu. One is to look for 'unexpected programs'. Sometimes you get infected and people install other programs besides viruses on your machine. This option will find them and ask if you really want them. Your product may or may not offer something like this.
'Spyware' is a class of software that gets installed on your Windows machines in all sorts of ways... including courtesy of whoever sells you your PC. You can delay installing spyware checkers until you have completed your re-install of Windows. Here's the description for one such piece of 'spyware':
Running Ad-aware and Spybot is optional. Your machine is 'safe' (not infected). If you are comfortable that someone is tracking what you do on your machine, then you can skip running these two programs. If you don't think you like this behavior, feel free to install the programs mentioned below and run them regularly (once a month). I ran these on my machines at home and while I have been very very careful, I still found 16 cases of 'low-risk' spyware.
There seem to be at least two freely available versions of spyware checkers that are popular, Ad-aware and Spybot. I'm told that neither finds everything, but together they do a good job. Both work similarly to virus scan programs in that they must get updates for the database of things to search for. Unlike virus scan software, these programs do not run all the time, but rather you must remember to invoke them once in a while.
This software is available from http://www.ada-ware.com/. The install is pretty normal. Once you start the program, you must first click on 'Check for updates'. It'd be better if the program would attempt this when you first start up, but it doesn't at least in the version I've seen.
This software is available from http://www.safer-networking.org/. The install is pretty normal. Its behavior is much like Ad-aware, but I find the interface less obvious. One nice feature is that it is aware of Ad-aware so it does not trip over things Ad-aware finds.
These two programs will not run themselves automatically. You need to remember to run them every once in a while. You'll have other maintenance things to do regularly and these scans could just be another thing to do.