Many times when downloading software, other programs that you are unaware ofcome with it. Malware writers often use the download as a way to transfer theirmalware into your PC.
The point here is to use caution whenever you are surfing around and visitingnew websites. The Internet is like a city. Some places are safe and others arenot. Unsafe places in a city have telltale indicators that you can see, butwebsites don't and therefore you need to treat unknown sites as if they aredangerous!
So in conclusion - an ounce of prevention is wortha pound of cure. The small amount of time and in some cases cost of installingand updating these programs is 'Nothing' compared to the time and effort ittakes to restore a compromised PC or to recover your identity after it's beenstolen!
Without fail - keep your antivirus and antimalware software constantly updatedand active!