Does non-existent father have the right?

Today I got a call from a friend of mine saying that my sons father is getting out of prison this month, has an attorney, has saved three years worth of work release pay, and is going to fight for his rights to my child!!!! My son is 7 1/2 yrs old and has only seen his bio dad once, when he was a newborn. Of the past 7 1/2 yrs, I beleive his bio dad was a free man approximately for 1 yr. The other 6 1/2 yrs he was incarcerated for various reasons, on two seperate occaisions. I have been happily married for 7 yrs, and we have 2 more children and one stepchild. We are a stable, happy family of five, and hope that things stay this way! What do we do now? I do not even know this person anymore. I am not going to lie down and let him interrupt, or possibly hurt my child or family. He has nothing to offer my son, and I am worried that he may do okay for awhile, then go back to jail, and hurt my son in the process. I have tried filing charges for abandonment, but incarceration does not count as abandonment here in Florida?! I will push for drug testing/couseling, anger management, supervised visitation, parenting cles, and anything else to keep my son safe. Bio dad says he is willing. He is a liar though, and I do not want him to emotionally damage my child. He tells people things like I am still writing him letters, which is absurd! That leads me to beleive that it is me that he is after, not my son. Can he even legally follow through with what he is planning? Should I even worry? What to do?