Legal Backfield Formation Rules: QB in Shotgun with 3+ Backs

Question
Is it legal to have a QB in shotgun and three additional backs in the backfield?  I thought I read somewhere that if a QB wasn't under center there could only be a total of 3 backs deeper than 5 yards in the backfield. I appreciate any insight here.

Answer
Shane
It is legal to have a QB in shotgun and three additional backs in the backfield.  For the formation to be legal the offensive team must have seven players on the Line of Scrimmage at the snap.  The rule used be be written that the offense could not have 5 or more players in the backfield.