|To monitor you computer there are Intrusion Detection Systems (IDS) that will monitor the communications your computer has with the internet. |
The problem is this is called White Hat Hacking and you must know what you are doing to do this kind of monitoring. Its called White Hat hacking because you have to learn how to be a hacker to stop a hacker. If you are not ready for this then just stick with Anti-Viruses.
That said here are some programs you can use. I recommend SNORT because it is free. This IDS will send email warnings to you when suspicious activity.
Also your system comes with tools to aid you like NETSTAT which will tell you what ports you have opened to the internet even when you are not browsing. Then you can take the IP addresses that it reports your computer connecting to and run a web site called WHO IS to see who the IP is registered to. If it is Google then it is probably ok, but if it is an Internet hub like L3 then you may want to block them on your firewall.
There is also TASKLIST which will tell you all of the apps and services that are running on the computer. I recommend you base line your computer. This means once you get every thing you need installed on your computer installed then you save your task list to a file for comparison. This way if you think something is running on your computer that should not be you can compare your current task list with your baseline to identify what is new so you can get rid of it.
You could also use HYJACKTHIS once you have a baseline to go through any programs that auto start and remove any bots that you do not want on your system.
Here are some links to things you might want to readup on...
I am sure others will post their techniques for securing their systems.