“Don’t buy Vista,” says the Microsoft advert, “unless you’re really, really serious about security.”

You won’t remember this advert, of course, because it never ran - not even five years ago, when Microsoft was, as it always seems to be, trying to wean users off an old operating system. And five years back, it was NT4 that people were being encouraged to move on from.

Back then, Microsoft favoured the stick rather than carrot: “No telephone support, updates, fixes or security patches will be issued and the only means of extended support will be via a private contract ­ usually an expensive option ­ forcing most buyers to seek an alternative system. Windows 98 will follow suit on 16 January next year and Windows NT Server 4.0 will lose support at the end of 2004,” wrote Martin Veitch at the time.

This year, Microsoft is trying to work out why ­ - as one of the vendor’s executives put it ­ - it is being forced to be its own biggest competitor by extending the life of Windows XP when, from the Redmond point of view, Vista is so much better. And as usual, senior execs are muttering about the ingratitude of users ­ - particularly professional users and tech support types ­ - and indignation is rife.

One internal blogger at Microsoft recently ranted about how hard it is to deliver the improved security that professional users are continually asking for, when those very same users always seem to begrudge having to learn about the new security features that Microsoft comes up with.

The good news is that this is probably the last time we’ll have to play out this little drama.

Vista, I’m sure, will eventually come to be a majority OS in the Microsoft stable, but “Son of Vista”, which is much closer to release than we realise, will struggle to force another round of upgrade payments out of corporate cheque-books. Not until Microsoft bows to the inevitable and adopts a com patible version of the industry standard of the coming decade ­ - a Unix variant ­ - will it find a way of carrying customers with it on upgrades.

And don’t tell me it can’t be done. Faced with no alternative, it simply has to be done.