Last month, Jim Allchin implied Vista was so secure it could be used without any anti-virus software. He quickly backtracked, claiming (with good justification, apparently) that his comments had been taken out of context and 're-interpreted'. But in the week Vista was released it turned out it was vulnerable to 39.7 percent of all malware currently circulating in the wild.

Some qualification for the above claims is required, of course:

[Sophos'] researchers found that though Vista's upgrade of Outlook could identify and stop all of the threats on the top ten list, Stratio, Netsky and MyDoom were all able to infect the system when e-mail was accessed via a third-party web email client.

I'm sure some people will be happy to point out that the security issue is not with the MS product, but with those of third party vendors, but I think that misses the point somewhat - you shouldn't have to spend a further £89.99 to realise the security benefits of your £184.99 'secure' OS, otherwise the security claims for the OS are, at best, a little disingenuous.