Some of the sites that offer you to watch free movies online use a script to collect your sensitive information, including any credit card you have used on that computer to pay your bills, and unless your credit card companies get your back on the fraudulent transactions you will find yourself in deep troubles.
The other way those sites might get you in trouble is by really finding yourself facing legal charges.
The famous example that took the Internet by
123movies storm a few years ago was when a woman illegally downloaded 24 copyrighted songs. Her sentence was $4 millions in fines!
That kind of sentence could financially break any middle class family.