The Patry Copyright Blog: Statute of Limitations: Part One, Infringement
Section 507, states that the defendant has 3 years to sue civil and 5 years to sue criminal, but according to this blog post, the court defines what counts as "accrual or commencement" based on each case. So your site may have been made three years ago, but only stopped infringing two years ago, you may still be liable. You can just sit and hope that they don't read this post and act sooner lol, or that if you do get sued the court will say that it was too far in the past.