Given the mathematical and algorithmic emphasis underlying computers and computation, it is unsurprising that many computer scientists and other computing professionals tend to think of a computer program fundamentally in terms of the algorithm it implements, and to carry that sense of abstraction over to the computer program itself. While that is often a helpful, or at least harmless, way of thinking, it is at root a categorical error.
An actual, functioning computer program is literally a physical entity. It occupies actual physical space, in RAM, disk, or other media; while one computer program occupies some particular space, nothing else can be there. A functioning computer program consumes actual energy as it executes, producing waste heat that must be dissipated by a cooling system. It doesn't matter if the same amount of waste heat is produced by an operating CPU regardless of what program happens to be running, what is essential is that when some particular program is running on some particular CPU, the energy that is consumed is consumed at the behest of that program.
What distinguishes digital software from most other organizations of matter is that in a computer it can be copied so quickly and easily at high fidelity; DNA molecules in a cell of course have the same property. The flip side in both cases is that either can also be easily erased. Computers provide an additional feature for software that cells at least in principle could provide for DNA but to my knowledge do not: The ability to transduce losslessly between the relatively stable matter-based representation and ephemeral, fast-moving wave forms.
For internetworked computers only the physical boundaries between separately owned and administered systems are truly fundamental. Despite the much-touted non-spatiality of `cyberspace', driven by precisely that lossless transduction, in fact each piece of hardware--each computer and disk, each wireline and switch--is locallized in space, and each piece of hardware has an owner. For small personal computers no less than huge corporate computing facilities, physical access and legal ownership are the two key elements defining a player in the game.