Once you've detected spyware or ad-ware it's very important to remove it out of your system due to spyware you would only see popup window with bunch of ads running but actually there is much more happening inside your computer which aren't even aware of.
Usually one installation brings many other spyware along with it which constantly keep on trying to change your computer setting without your knowledge.
Which can cause some of your programs stop functioning and it's common that certain functionality is suddenly missing in your windows or in any of your installed programs.
Spyware usually attack your browser which is internet explorer, FireFox depending on which browser your use.
It usually add book mark links to your browser and change your default homepage that is less harmful things that it can do.
Sometime it can completely hack your computer which can result in slowing down of your computer & identity theft.
There are couple of things I listed below one can do to fight back with spyware: Step 1.
If you are using Microsoft internet explorer then replacing it with FireFox browser which would decrease infections dramatically.
Step 2.
Some programs add themselves in to installed software on your computer.
You can remove those infections easily by going to "add/remove software tool" of your computer and just uninstall them the spyware.
Step3.
Here comes the complicated part some aren't that easy to remove out of your system and therefore to remove them you must need a removal tool to completely sweep those infections out of your system.
Those anti spyware removal tools also keep you protected against spyware and ad-ware.