There are many different types of malicious files and software that are written for the Windows operating system.
Most of the time people think of these as viruses and spyware.
These can hurt your system on the software level as well as the hardware level.
They can also spy on what you do on your computer making you have privacy issues.
One thing that many are not aware of are things called botnets.
Botnets are scripts that run in the background on your machine using your computer's resources and your internet connection to run automated tasks.
One of the most common uses of this technology is to send out spam email from your machine.
There are millions of computers with this type of problem on it and many are not even aware that it's happening.
The first thing that you need to do to protect yourself is to always have on the latest and most updated virus protection software.
If you always keep this updated, you have a much higher chance of keeping these types of malicious programs off your machine.
If you aren't sure if you have one or not, you can scan your computer's bandwidth transfer.
If you are sending and receiving data when you don't have your browser open, it's a big sign that you could have a botnet on your machine.
Try using your virus protection in safe mode doing a full scan to get it off your system.
At times in safe mode the botnet program won't have a chance to boot and is easier to remove.
As a last resort, you can always install the operating system again.
This guarantees that you won't have a botnet issue once you get everything installed again.
Do your best to then protect yourself to keep these off your system in the future.