Of course the next time it rains heavily some of your little vans do crash and cause damage and upset.
So, who is at fault here? I think it is fair to say that your delivery company is more than a bit to blame. Of course it would have caused you difficulty and upset to fix your vans. And you can argue that there should never have been a fault with the vans in the first place. But I think in this situation any company would have made darned sure that the problem did not arise.
The Sasser virus upset is exactly the same situation. Except that companies who rely on computer support do not take their computers as seriously as their little vans. Viruses are just like the weather. Now and again you get a hurricane. Now and again some buffoon thinks it "might be neat" to send something out on the internet and see what happens.
If I lose a seat on a plane because of the Sasser virus, I'm not going to be chasing an 18 year old German idiot, I'm going to be banging the desk at the checkout shouting about the duty of care owed me by the airline to make sure that their systems don't fail in this way (and hoping that their maintenance policy for their airplanes is somewhat more rigorous...)