They did this when they shipped iPods with windows viruses on them. Instead of just biting the bullet and putting an outright appology, they actually had the gall to blame microsoft for allowing viruses on their systems (when they were the ones spreading the virus in the first place!).
Well, the one spreading the virus in the first place was someone making spot checks of iPods to see if they were working correctly, using a Windows machine to do this, and that PC was infected by a virus and copied the virus to the iPods.
You are quite correct that whoever was responsible for having this PC infected should take a lot of the blame; it is hard to say whether Apple should be blamed for not finding the viruses because the virus was actually added in the process of checking the iPods. You could surely blame them for using Windows anywhere in the process of making iPods - which is what Jobs did.