I think you are spot-on Conran, it is increasing dramatically. One of the biggest issues is that so many computers (PCs and servers) are not updated and/or protected, so bot-nets are increasingly more available making them cheaper and easier to find. And its those bot-nets that hackers use to get into sites and get past the security.

I read once that if every windows user was forced to upgrade with the latest patches, the amount of bot-net computers would decrease by something crazy like 95%. Then it would just leave unpatched servers, which are easier to fix up as they are somewhat more controlled. That's why I always keep updated with any patches for both my home computers as well as for any scripts that I run on my servers (the main culprit there being WP itself).