[MaSnaka]

CSXDreamer is right,

Most door jams are the 3/4" thick pine. Behind that is a 2x4 trimmer and then a 2x4 king stud. If the door jam is shimmed excessivley because of a loose fit in the rough opening your screws may be too short. As a carpenter I find most of the entry doors on peoples homes do not have the reinforcing brackets and the 4" long screws installed in the strikes. They are provided with the better quality deadbolt locksets but I think that installers get lazy and discard them rather than install them. That leaves the 3/4" door jam and 3/4" screws to do the job. Easy break in. With the 4" screws you are bolted into the framing and that makes your door that much more secure. But we still have windows so anybody that knows how to break in will do it.

John