Wnat can I do if I purchased a business but later found out the way it was being run was illegal?

There are a few things you may want to consider/pursue.  First, you will want to ensure that so long as you are running the business, it is in compliance and not being run illegally so as to avoid risk going forward.  You may be able to pursue a rescission of the contract or a breach of contract theory against the seller of the business if they induced you to proceed with the transaction by fraud.