The true cost of hacking, IMHO, covers everyone, not just businesses and not just homeowners. There's so many discovered hacks nowadays, coupled with spam email, aligned with spyware, etc..it's not even funny.

If I were going to ask the question of what it would cost, I'd first rephrase the question to "What's the cost of hacked systems, spyware, spam, and the like?".

Some people say it's the duty of the vendors and software companies and even the resellers (HP/Gateway/etc) to ensure that Windows is more secure because getting patches is hard, not user-friendly, a long download for those on 56k, etc..the list of excuses goes on and on. For a hacked system that a homeowner has that could've been prevented had it been patched, the cost is very little. When you consider how many get taken every day, that cost exponentially increases. One would think it'd be prudent for said homeowner to "learn" something, but hey, that might be asking too much nowadays.

Businesses are somewhat in the same boat. So many companies now have such a long time to get something done, it's not even funny. Our "change management" team has to approve anything that goes on in the computer section of the company and it takes a good two weeks for them to do anything. What does this do? This puts us two weeks behind the curve and it's supposed to be our fault if something gets broken in the meantime? Rather unfair for us, don't you think?

Hacking systems and the downtime created from spam email and spyware cost a company quite a bit in lost time, resources, etc. However, when given the option to negate a lot of those costs by fixing the problems, they don't. Because of the cost of improved systems, improved software through patches and newer releases, and various other ways (hardware firewalls, etc), they'd rather "invest" that money elsewhere (sales, etc). So who's fault is it then?

All in all, I guess it would be costly across the board simply because so many computrers all have the same OS (XP/2000/etc) in elements of lost time, lost machine access, lost ISP time (shut off accounts/etc), fried OSes which results in reinstalls, etc...