I don't write the software I point out, most of it is provided by like minded individuals to help you they too like their privacy. My procedures continually adapt and evolve to take into consideration the worlds threats but if you follow my simple advice and use a couple of these tools it makes the world a safer place for you and the people your computer can be used to attack.

What you need to do on EVERY computer that connects to the internet.

You need to find out what is running on your computer NOW!

1. Sneak a peak under the hood - First determine what is actually running, unfortunately Windows doesn't have a good tool for this. So I would download the freeware Trend Micro Hijackthis to see what is actually running.

Hijackthis Download

After you acquire hijackthis create a folder for it and then run it from that location.
The folder is needed to keep the backup files for any changes that it does.

Now the scary part there are many programs that are supposed to start up and thieves will cleverly name their programs to be identical to the required ones with only small differences in where they are located on your computer to show that they are. Go line by line through he running applications and "google" the application name for the ones you don't recognize, if you cannot find it there either its a bad piece of software or a new version of good software use your best judgment and back up often.

2. Spyware in the background - Download Spybot, run through its internet update cycle, then use the immunize function against bad programs, then run its search for the "badware", again always make backups and don't delete anything your not sure of  :-) I guarantee you will not regret making backups often.

Spybot on Download.com   Why download.com? I find some interesting individuals spam the search engines so that core site is hard to spot and tends to be hidden in malware sites due to that. Success can be brutal sometimes.

3. Antivirus - I use a couple to just make sure,  here are some free online scan links:

Panda Software

Mcafee

Trend Micro

4. Software firewall's - I use a free basic firewall from zone alarm to catch any weirdness not known yet in the wild. As it only takes about 20 seconds to get a bad worm on an unpatched XP system.

Free Comodo Firewall / Anti-Virus

Free Zone Alarm Firewall

5. Pop-ups - Turn off the messenger program in windows. I use the free utility "Shoot the messenger" by Steve Gibson at Gibson Research. His site is also great reading on internet privacy and security issues.

Shoot the Messenger Utility

6. More popups - Free popup blocker - Google has a wonderful toolbar for Internet Explorer. If you need a popup then simply hold the control key down and then refresh the page. Works like a charm for me. 

Google Toolbar

I also have started to fall in love with Mozilla's new Firebird browser (now obviously called Firefox), the tab feature is worth it by itself but it also blocks all sorts of popups and there are numerous extensions that are not included in the first install but easily added as you wish

Google Chrome Browser has evolved at light speed and in 2010 has been my primary browser, the addition of many common plugins easily starts to catch up with Firefox and Internet Explorer.

7. Hardware firewall's - these are not free and most likely if you can download it, its not what I am talking about. A basic hardware firewall will only cost you $20-$50 and will likely save you hours of your valuable time in the future. It typically has four network ports and one port to connect to your dsl or cable modems, they also make these for dial up and isdn modems as well.

I go for cheap and easy, search Ebay or pricewatch.com for "firewall 4 port" good deals on new ones. Dlink and netgear are my favored (if their is such a thing as "favored") this week but Compusa's white box special is also fine.

Also if your a tinkerer check out the Tomato Firmware replacement, tons of really neat options for common hardware.

8. DNS Server Solutions -  Allot of malware or bad sites can be stopped if you have the right dns servers, I use Opendns.com free solution to help me control the quality of websites my networks are on. 

Get Started on OpenDns

Hope this helps!

Disclaimer - This is merely what I did on computers under my control, any advice here is just that advice and will not work and likely cause great problems if any one of the situations is different than the one I am in. Use at your own risk.