A quarter of UK users?
I have never met anyone that would have done this.
I have spent many an hour fixing problems for other people caused by simply not having common sense when browsing - people that click Yes on the pop up windows, or people that download software from Kazaa, or even use Kazaa for that matter. Or people that actually save attachments from people they don't know.
I like Linux, but I use a Windows XP machine almost every day (at home), I have an up-to-date virus scanner and a collection of spyware watching tools - and of course I only use Firefox and Thunderbird.
And when it comes to email; if the mail is not from a known contact, but has somehow slipped through the spam filter, I don't even bother reading it. As such I very rarely get anything for me to be concerned about. (Touch wood)
Off the top of my head I would say that everyone I have spoken to that has had a problem in the last say 4 months has been a problem that is directly related to downloading any old rubbish from p2p services - and unfortunately some of these people have had similar problems before and will have those problems in the future - they just don't think about what they are doing. And even worse is that even when they have had to learn the hard way, they still go back.
But back to the point, if you know anyone that falls into said 'quarter' that lives in Bristol, please forward their details I'll keep an eye on thier garbage - I could keep the good stuff and sell the rest on eBay