How can I know whether torrents I download do not contain some sort of keylogger?

Say I download some software off thepiratebay, when I am installing that software I have this fear I am also installing some sort of keylogger/spy software and everything I do on my computer from here on will be watched by some computer hacker. How would I know if this was true and how likely is that to be true? It makes perfect sense. If you are that sort of criminal, just incorporate your spy software with whatever software people that is popular and lots of people will download and you have access to all of their computers almost willingly.