The mystery of the spy wire

Since we are replacing the ceiling and the lighting in our basement, Jeff has ripped out the old ceiling. Inside we found a big bundle of 9 cables. These cables look new. They are taped together and run across most of the bedroom ceiling. One cable splits off and goes down one of the walls where it emerged in a junction box that was covered by a blank plate. Two of the cables split off and go toward the two upstairs bedrooms. The other six go up through a hole in the ceiling, into the closet of the kids' room upstairs, and are visible in the closet corner. They go up into the attic and presumably out somewhere. I haven't investigated that far.

I was curious what these cables are. Here's a photo of one end. You can see it has about 10 smaller wires in it.Jeff took a piece with him to Lowes to see if they could tell him what it was for. He said there were about 8 associates, plus the store manager, looking at it. They finally decided it was CAT-5, which is used for security systems and ethernet. Huh? Why on earth would the Tervorts have the entire house wired with ethernet and not have one single ethernet receptacle? Jeff thinks that maybe they had a security system installed at some point, but that doesn't make sense to me either. There is no other indication in this whole house of a security system attached (or formerly attached) to any windows or doors.

This house drives me bonkers.