Which is precisely the point. Since over 54% of all Windows users are currently using XP, viruses, malware, and spyware remain a seriously daunting issue for Windows.
Perhaps, however these adverts are targeted at people buying new machines, the vast majority of which will most certainly not have XP on them.
User installed trojans are no where as debilitating as worms like conficker.
That's not actually true. There are some harmless worms and some really horrible trojans. It's not the delivery method that is important here, it's what it does.
You want to portray this image of a mac box being hooked up to the internet completly naked (without antivirus) and subsequently getting taken over within the hour and infested with malware, which isn't the case.
It's actually the case with any of the current generation major operating systems. None of them are likely to become infected without user intervention.
Likewise the users wern't at fault for something like conficker unless they refused to patch their machines once it start to spread. That was microshafts fault for having the exploit in the first place.
That's a ridiculously silly thing to say. Microsoft patched the Conficker vulnerability months before it's release. Those users who became infected had plenty of notice and the blame lies squarely with them in the same way it would lie with anyone who refused to update OS X security and ran into all sorts of bother as a result.
On another note, the market share argument is completely ludicrous. This is basically equivalent to saying that there are no incentives to design viruses for Macs.
Actually it is and it isn't. It's ludicrous because OS X did have considerably better inherent virus protection than Windows right up to Vista's release. MS were about seven years behind Apple in this respect. Therefore whilst you'll see a lot of viruses for XP you won't see a lot for Vista or W7 because it's as secure - or arguably more secure - than OS X. It's just a shame it took them seven years to get there.
It isn't ludicrous because form a malware point of view - and I'm talking about trojans and worms which require user intervention and, as such, are pretty much platform neutral - Windows does get far more of these purely because of its dominant position in the industry.
So kind of a mixture of both really.
That error message about a potentially misleading package is to prevent self-infliction of trojans...not really anything to do with viruses. Yes the bottom line is that all hell can potentially break loose, but the day that a virus appears in OS X to destroy a whole network with no user intervention is the day hell freezes over.
Sure, the same applies to Vista and W7 networks. Now XP, which is a horror that needs to die, is a different matter.