There was a web firestorm yesterday over an apparent warning from Apple that its users could be vulnerable to attack and should consider installing anti-virus software. It was a firestorm that we helped to fan with a story - and a post on this blog.

Now it appears that the story was old and that the message on the Apple support site, posted on 21 November, may have simply been an update of an advisory note published back in 2007. What's more, the November message has now been removed - with no explanation.

So I'm sorry if we suggested that this was a major U-turn by Apple when it was not. Graham Cluley, who we quoted in the post, now describes the incident as "a fascinating example of how the internet can get carried away with itself", and it is certainly true that bloggers and journalists (and I include myself) hate to be left out when this kind of storm brews up.

But Mr Cluley stands by his view that Mac users should not be complacent about their security: "Yes, the news that Apple is urging people to run anti-virus software isn't actually news... apart from for the people who didn't realise they had to run anti-virus software on their Apple Macs! - which seems to be quite a lot". It is worth noting that Mr Cluley's firm Sophos sells an anti-virus package for Macs and is presumably keen to boost its sales. I have to confess, as someone who has used both Macs and PCs for the last 12 years, that I have never installed any extra security on my Macs, and I'm still not convinved that I need to act.

And one thing that this incident does show is Apple's split personality when it comes to communicating with its users and with the media. On the one hand, when it has a positive story to tell, it is brilliant at sending simple, bold messages to consumers and skilful in projecting its case to the media.

On the other, when things go wrong - complaints about scratched iPods or concerns about Steve Jobs' health - this is a company which retreats into the Cupertino bunker, closes the door and says nothing.

So I contacted the Apple PR department at 1115 GMT on Tuesday to seek a comment on the story. Back they came twenty minutes later, with a promise to look into it and "keep you posted". 23 hours later, I'm still waiting. So what is Apple's advice to customers on whether there is any need to install anti-virus software? I'm still not clear - are you?

Update Wednesday 1334: Have heard from Apple this morning - Macworld has a statement from Apple spokesman Bill Evans.

Update Wednesday 1041: Please see my follow-up post.

Oh dear - even as I write this, I can see the smug smile spreading across the faces of Windows users - and I can hear the clatter of keyboards as thousands of Mac fans compose angry messages. But here we go - Macs are not immune from internet infections, and that's official [story updated since original post].

The news came on 21 November when Apple put up a little note on its support site [link no longer live - see follow-up post], explaining that "Apple encourages the widespread use of multiple antivirus utilities." The company did not highlight this warning, and in fact nobody noticed it for some days. Now it's become a big story, and reignited the row about the respective strengths and weaknesses of Mac and Windows when it comes to security.

Because the one thing you have never needed to worry about when you get an Apple computer is spending money on expensive anti-virus software. What's more, you are not continually pestered with those annoying pop-ups asking you if you've updated the security package.

The lack of viruses and other malware targeted at the Mac OS was largely due to its relatively small share of the PC market - if you're an ambitious virus writer you want to aim at the largest possible "audience" and that means Windows users. But as Macs win a bigger share of the market, they present a more attractive target.

Now Apple seems to be telling its customers that the golden age of innocence is over, and they will have to start shoring up their defences. It's even directing them towards a couple of anti-virus products on sale in its own store. Many will ignore that - and wonder if this is just another marketing ploy by the security industry.

So do they need to worry? I've spoken to a couple of security experts.

Greg Day at McAfee admitted that the threat to Mac users was relatively tiny compared to that faced by someone using Windows. "There are about 10 million unique 'threats' in the Windows space," he told me, "compared with about 150 threats to the Mac OS." But he went on to explain that a lot of new malware was now targeted not at an operating system but at cross-platform applications, like web browsers, and that meant there was a growing threat to Mac users. "It is common sense to take precautions, even if the threat is relatively small."

Graham Cluley of Sophos pointed out that his firm had been turning up examples of Mac OS malware for some time. One recent case involved a bogus webpage, supposedly containing a video, which then directed users to download some code to enable them to watch the movie. Not a good idea, of course.

Mr Cluley says the Mac malware threat is "still a raindrop in a thunderstorm compared to Windows" but he says there are still good reasons to take precautions. "The Mac is no longer the safe haven that people think it is." That's partly, he says, because a lot of new people are coming to the Apple platform." It's no longer just black polo-neck wearing, cappuccino drinking, beardy zealots," he said, in a phrase which will effortlessly offend millions of Mac fans. "There are a lot of naive new users - so there will be people writing malware who will see that as an opportunity."

Now it's obviously in the interest of security firms to play up the threat as they try to invade the one section of the computer market which has so far resisted their blandishments. But it's interesting to see Apple also promoting that message. Mind you, it's just the support team saying it very quietly at the moment. I've just watched the "I'm a Mac, I'm a PC" advert which shows the PC guy coughing, spluttering and falling over, while the cool Mac guy remains immune to his virus. I wonder whether Apple's marketing department will decide that's a line which doesn't play so well any more?

Update: Comments are open in this updated post.