I would need to know more about the structure to your site. If you are a service provider of a forum allowing users to post content (like YouTube), you would be regulated by the DMCA (digital millennium copyright act). If you stick to those regulations, you can avoid liability. Otherwise, disclaimers of liability alone likely won't cut it. Consult a copyright attorney.
You need to see an Internet attorney. If you are replaying a Napster 1 business model you are illegal. If you are just hosting like You Tube you might read 17 USC 512 so you will understand better.
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Terms and conditions of use for website users, generally, will not protect you from a third party lawsuit. While you may have a right to indemnification from a user who violates your terms and conditions by posting copyrighted materials, you will still have to retain counsel and answer a lawsuit if you or your site is named as a defendant. Your best bet would be to contact an intellectual property attorney in Boston (there are a TON of them), and seek counsel as to the best way to legally protect yourself from internet scofflaws. Good luck!
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