You cannot really tell if a site is installing spyware unless they have a pop up that asks you to install something. If that happens it is a pretty good chance that they are installing spyware, I would say 90 to 95 percent of the time. A good rule odf thumb is to never click yes when you are asked to install something. Now having said that they are times when you have to let a site install something, but always make sure.

Ad-aware is a good program for detecting spyware and the base program is free. There are a few others like spybot that are also pretty good and free.

There are some programs that you can get on your computer called malware that do things like actually change your homepage that ad-aware will not take care of. Just to give you a little warning.

I hope this helps.