The criteria for responsibility is cause and effect. If one entity was not present or did not perform an action (or held an inaction), and the problematic event did not occur, than that entity is responsible.
Victims should not deserve any benefit of lax criticism solely for being a victim. Furthermore, those who wrongfully claim to be a victim when they are not victims are clearly liars.
In this case, the victim is not just the hospital. The victims are also the patients of this hospital. However, the patients were at more of a loss than the hospital itself. There has been little discussion of how the hospital staff should be protecting the patients from this attack. The staff is complacent in their inability to protect the integrity of the hospital and, more importantly, the well being of the patients.
Consider the following examples. If a hospital did not use use sterile equiptment and patients become infected with a pathogen, should the hospital be responsible, or should the pathogen be responsible. By your logic, the pathogen will be responsible. However, the hospital is clearly at fault here.
If a network of computers becomes zombies after an individual invades them, would you consider the owners of the computers to be at fault? Clearly, you might not. However the computers are similar to pets of an owner. If a pet kills a person, the owner is also at fault. Similarly, the owners of the computer(s) are also at at fault because their property is being used, addendum a hypothesis that the zombies are to be used in an invasive act, should be partially responsible. If one does not believe that the computer owners are at fault, then one can not support laws of most Western societies in their entirety.