One of the best ways to know if your system has been hacked is to go to the Task Manager. When you are on your system and it is slow or lagging, go there and see what other programs are running in the background. If you see something that you are not sure of, Google it, read what it is. If it is a bogus program, like adware, simply stop the process. Now you have the fun task of finding the file that is causing all of your problems.